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Measuring practical heat conductivity - Cast iron, aluminum, copper

A couple months ago, I posted that I had stopped using most cast iron mostly because of its uneven heating. I still sear steaks in a large skillet and occasionally fry an egg or two, but that's about it:


In response to one of the comments, I stated that I had observed greater than 100 degree F differences in the surface temperature of cast iron, even pre-heated. A few commenters asked me for details, since they were surprised by the magnitude of the heat difference. At the time, I had just observed differences informally.

Anyhow, I ran a few quick tests today, and below are the results. I have to admit that I was a bit shocked how poorly cast iron performed, which was even worse that I expected. I've always been aware of its poor conductivity, but finding up to 200-degree differences between center and outer bottom of a preheated pan is pretty crazy. It does explain why I've found it impossible to cook just about anything evenly in it over the years, except when stirring constantly.

I'm not trying to convince anyone not to use cast iron (for years I babied my stuff and used it almost every day), but I do think those who use it need to be aware of what they're up against. Obviously moving food around in a pan (particularly liquids) will even the temperature out a bit, but cast iron still seems a pretty poor choice for most general purpose cooking, if you're looking for evenness. (I'm not disputing its good uses for browning, searing, non-stick cooking, etc.


I tested four pans primarily, all roughly the same thickness:
(1) a large vintage tin-lined copper saute pan, about 9.5" in diameter
(2) an aluminum griddle with non-stick coating, about 12" in diameter
(3) two well-seasoned standard 10" Lodge skillets (I have two, many years different in age, and I wanted to prove that I didn't just have one dud pan)

I turned my gas stove to low and pre-heated each pan in turn, observing the changes over 10-15 minutes with an infrared thermometer. I waited until the pan temperatures were reasonably stable. I kept the burner at the exact same setting each time, just changing pans.

The results for the stable temperatures after 10-15 minutes shocked me a bit:
(1) Copper: center ~225F, edges ~190-200F
(2) Aluminum: center ~280F, edges ~215-230F
(3) Cast iron: center ~400F, edges ~200-300F

When I say "edges," I mean near the edge of the bottom of the pan, not counting the sides. Notably, for the copper pan, even the top lip of the side was less than 50 degrees off from the center of the pan, whereas the top of the cast iron sides were off by more than 250 degrees, even after 10-15 minutes of preheating. (I did a brief test on a copper saucier, and saw a similar pattern -- even though most of the pan was sloped above the burner, the top of the sides was rarely more than 50 degrees off from the center of pan on the burner.)

Note that the cast iron was incredibly uneven, with the bottom of a 10" pan varying by 200 degrees even after well preheated, and even though the pan was centered on the burner, the temperature near the sides varied by almost 100 degrees from one side to another. There were also plenty of hot spots all around the pan where temperatures varied by 50 degrees within an inch or two. (Both skillets showed similar unevenness.)

These differences remained relatively constant while the pans were preheating. Copper was consistently about 30 degrees hotter in center than sides, aluminum 50-60 or so, cast iron, 100-200. I had expected that preheating on low would give cast iron the best chance, but it still displayed variance of hundreds of degrees.

I did brief trials over medium and high heat, but I didn't try to heat to equilibrium, because I don't like to preheat empty pans to over 400F except for searing purposes. In general, I observed similar patterns in terms of the differentials between center and sides at higher temperatures.

I did try heating the cast iron to quite hot, since I do that for searing. Over high heat, the temperature differential was slightly better at first, I think because the burner flares out more on high heat. But it still was always greater than 100 degrees different across the bottom of the pan. And once the center got above 500F or so, I started seeing 150-200 degree differences again for the edges. At 700F in the center, the outer edges were even below 450-550F, but I expected that.

I briefly tried putting my cast iron dutch oven on the stovetop, as well as a cast iron griddle, and I saw similar patterns, so it isn't just two dud skillets.

Now I know why I could never get my pancakes to be done evenly on any cast iron pan/griddle, no matter what I tried. One could always preheat in the oven to obtain a consistent temperature at first, but once returned to the stovetop, you'd only have a few minutes of relatively even heating.

I'd be interested in hearing in others have tried measuring temperatures in their pans and if they've seen similar results.

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  1. Thanks for the data. Very interesting about cast. The <50-degree difference with copper does not surprise me, but expect criticism about your methodology, however well-designed.

    I'm wondering... Why didn't you run straight SS or clad pans in the race? Many here claim it a virtue that SS pans have high bottom-to-lip temperature gradients. I'd be VERY interested to see the real-world temperature results, both on the pans' walls and around the bottoms.

    Thanks again!

    6 Replies
    1. re: kaleokahu

      I don't claim that my methodology is anything special -- I just did some simple tests in response to some inquiries on a previous post that got me curious. Of course I don't claim high accuracy. I've basically satisfied myself as to the reason why I had so much trouble cooking things evenly in cast iron, which is all I set out to do.

      I also wanted to come up with a general range of temperatures to expect on a pan surface based on conductivity. While I've occasionally pointed my infrared thermometer at my cast iron skillet, I've never paid much attention except to get it up to an appropriate searing temperature. I expected 100-ish degree difference, but not 200, particularly under constant heating for more than a couple minutes.

      As for materials, I was mainly interested in cast iron, and I just chose two pans with roughly the same diameter that I had handy and would make a contrast in conductivity. I could try other things, but I didn't want this to turn into an all-day project. :)

      1. re: athanasius

        athanasius: I was being laudatory, not critical. This is the kind of real-world testing that is needed. My point about methodology was my way of warning you, tongue-in-cheek, that folks on this board won't gladly suffer their dogma being challenged.

        I lack your infared thermometer gun, else I'd do your test on clad and SS myself.

        1. re: kaleokahu

          "that folks on this board won't gladly suffer their dogma being challenged"

          You are asking for a fight, aren't you?

          1. re: Chemicalkinetics

            LOL, I seem to get fights here whether I ask for them or not. 2xLOL, I was also referring to myself; yes, the occasional self-tussle can be fun, too.

            I remember that Escoffier famously commented on the primacy of culinary empiricism and the limitations of culinary theory. I will dig it up tomorrow, my paraphrase would be like cooking in stainless steel.

          2. re: kaleokahu

            kaleokahu - I understood. I was just trying to matter-of-factly mention what my goals were. Sorry if it came across any other way. Thanks for the kind words, though.

      2. My only question is whether you're sure the heat variance in your cast iron is from the cast iron and not due to your burner? On those occasions when I find one part of my cast iron pans aren't browning things as rapidly as the rest of the surface, rotating the pan about a quarter turn takes care of the problem for me, though I do hve to rotate it back and forth regularly. I currently have ribbon-under-glass burners, and in the past have cooked with standard electric coil burners and with gas. Gas produced the most even heat in my cast iron. As for the cooler perimeter in your cast iron, are you sure you have it on a large enough burner?

        38 Replies
        1. re: Caroline1

          Careful now, Car! You weren't suggesting there at the end that a copper pan can more evenly cook your food even if it's on an undersized hob, were you? (Sorry, I couldn't resist)

          1. re: kaleokahu

            No, I was suggesting that when even heat distribution is critical, I get out my butane burner and crank it up under my cast iron! '-)

          2. re: Caroline1

            I thought of this, and yes, the unevenness on the edges seems to have something to do with directionality in my burners, but only to a limited extent. If I rotate the cast iron periodically, I can get the edges less than 200 degrees off from center, but not much less than 150, and certainly not less than 100.

            In any case, the directionality effect seems to be markedly less for the aluminum and copper. For copper, I was seeing about 5-10 degrees difference on opposite edges, as opposed to 100 degrees for cast iron.

            But the fact remains that the CENTER of the pan is always about 100 degrees off from the edges, unless I offset the pan on the burner.

            Am I sure I had it on a large enough burner? I don't have giant burners. I have standard gas burners on my stove, about the size I've seen in most homes. I'm not testing this on a professional stove, just a typical home model. The behavior in my skillets hasn't changed since I lived in two previous apartments either, both of which had gas stoves with similar sized burners. And I didn't test a giant cast iron skillet -- I just used the standard Lodge 10". Even on a large burner, I'd imagine a 12" or larger skillet would experience similar problems.

            I'm not at all disputing you would get more even heating on a larger burner. I was wondering what the typical response is on a typical home gas burner, which is what I have.

            1. re: athanasius

              Interesting. When I had a gas stove, I never checked out the actual surface temperatures but just judged by how evenly things like pancakes were browning. The turning of the pan to adjust for heat has only happened with electric burners, not with gas that I can remember. Curious.

              1. re: Caroline1

                I suspect the unevenness is caused on my stove because of the direction of the gas line, which points outward on both sides (toward the back on the back burner and toward the front on the front burner). I mostly observed higher edge temperatures on the front of the pans, and I was using the front burner for the tests.

                I can't see a visible difference in the burner (it's not like flames are higher on one side), but obviously gas under pressure is coming out from a particular direction and will have more momentum in that direction. The differences for the copper and aluminum were negligible in this regard, but cast iron's slower response will register cumulative effects like this better.

                I didn't expect this either on my gas stove and never noticed it much before.

            2. re: Caroline1

              Actually, on second thought, I don't know if a larger burner solves the problem, at least on a typical gas stove.

              I remember now a pattern that I've noticed when I heat my cast iron on high for searing purposes. With my thermometer I quickly begin to see a cold spot develop in the dead center of the pan, since the flames of the burner fan out more when it is on high than low. It's not as big as the differential to the sides of the pan, but it's as much of an issue as the hot spots I usually see.

              So, I think a typical large gas burner will only lead to different problems in terms of evenness. The only way I see to get around these problems is constant motion of the pan, which is fine when cooking an omelet for a minute, but gets tedious for longer cooking.

              Of course, a large electric heating element would produce more even heating in this case (or, for that matter, a large bed of charcoal or any other even heat source), but then you have the problem of response time for most electric stoves, which would slow down the already slow response time of cast iron even more.

              1. re: athanasius

                I don't think you are correct here. The problem is how to explain it....

                A round pan will always conduct better from the outside of toward the center than vice versa. There's a reason that the heat differential is not as big from sides to center when using high heat (large ring of fire) as from center to sides when using low heat (small ring). Essentially, the center of a ring, when heated from the outside, will receive conducted heat from more directions than the outside of a ring heated from the center.

                Probably your small burner is a ring, right? Meaning that the very center is not heated. But when you used the IR thermometer on low heat, you didn't notice a temp-drop off at the very center, did you? The center, though not directly heated, was probably as hot as the small ring directly on top of the fire. But if you were to check the temperature outside that ring - as far outside the ring as the center is within - there will be a noticeable decline in temperature. This is the effect I'm talking about.

                I know that doesn't make a whole lot of sense, and I tried to find a graphic that would illustrate it (rather easily, actually) and failed. If anyone can explain it better than I can, please step in. But the point is that small burners on low heat with large pans lead to bigger temperature differences within the pan.

                1. re: cowboyardee

                  I think I understand your point, which is valid. Perhaps it has something to do with there being substantially more surface area (floor AND walls) to heat OUTSIDE a circular gas ring than INSIDE it. But I think a larger single-ring gas hob is mostly just going to change where the unevenness occurs. Maybe there's a "sweet spot" in ring diameter that would minimize unevenness, but if so that's going to vary on a pan-to-pan basis, don't you think?

                  For me, the "take home" of this test is that cast on gas rings is going to be uneven, so long as there aren't jets licking the pan ALL OVER. I have seen VERY large (i.e. 30-inch diameter) stand-alone industrial hobs that have concentric rings of jets that can be individually valved on/off to size the jetted area to the bottom of different vessels. I think something near to that complicated and expensive (tens of thousands of $$) would be required to solve this problem with cast. Not something likely to make its way into our kitchens.

                  1. re: kaleokahu

                    "Perhaps it has something to do with there being substantially more surface area (floor AND walls) to heat OUTSIDE a circular gas ring than INSIDE it"
                    In reality this is true. But it's not the extent of it. Heating from the outside causes less unevenness, but it's primarily because of the direction of conduction. There will be more conducted heat focused on the center of a ring than at an equal-distant point outside the ring. This would be easy to illustrate with string of Christmas lights formed into a ring (even though light and heat conduction don't really work quite the same way). This is why you won't see burners with one, strong, centralized flame.

                    "but if so that's going to vary on a pan-to-pan basis, don't you think?"
                    It's gonna vary with the diameter of the pan. Real high end stoves have some burners made for 12 inchers, some for smaller pans. Pan size is comparatively standardized.

                    1. re: kaleokahu

                      "For me, the "take home" of this test is that cast on gas rings is going to be uneven, so long as there aren't jets licking the pan ALL OVER."

                      I know this is late, but to make my point clearer, what I'm arguing is that if you heated a pan evenly all over, after a short while you actually won't get an evenly heated pan, but a pan whose center is far hotter than it's edges. There HAS to be more heat applied to the outside than to the center for even heating.

                      1. re: cowboyardee

                        I think you have been clear. I just happen to disagree.

                        If you had jets licking every square centimeter of the pan bottom, you would have very even heat. Not perfect, perhaps (because of the "toward the center" phenomenon you so well describe, but also because the unheated walls are drawing some of the heat away at the borders), but far more even than any single ring arrangement would provide. But we're 'WAY out on a theoretical limb here, because few folks at home have wide pro hobs, let alone multiple rings.

                        I do have a triple-ring crab boiler, and I'm sure I can find a cast skillet sized so I can flame it evenly across the whole bottom. If I can lay hands on an IR gun, we'll see if I'm wrong. If I can't, would you be satisfied with the "flour test"?

                        1. re: kaleokahu

                          "I do have a triple-ring crab boiler, and I'm sure I can find a cast skillet sized so I can flame it evenly across the whole bottom."
                          A triple ring crap boiler does apply more heat to the outside than to the direct center of the pan. I'm not trying to argue with you - I just get the impression you're misunderstanding me, or at least misrepresenting my posts. I'm not claiming a single ring is the best way to evenly heat a pan - far from it. The most even way to heat a pan would certainly be with flames all over, but also with more intensity towards the outside of the pan than the center (even more theoretically, it would be best to start with completely even heat and then slowly increase the intensity toward the outside of the pan).

                          "But we're 'WAY out on a theoretical limb here"
                          I'm sorry if I wasn't clear - I thought it was obvious I was babbling mostly in theory all along. The entire practical element of my posts could be boiled down to 'them wide pro-style burners sure are nice. One day I'm gonna get me one and never burn my pancakes again!'

                          1. re: cowboyardee

                            10xLOL... If you have a QWERTY keyboard (the "B" being far from the "P"), I'm very concerned--incinerating toilets and coprophillia are not my specialties.

                            [Along these lines, I once had a court case involving sewer construction. My opponent persisted in referring to the contents of the pipe as the "affluent". To this day I cannot get the picture of bejewelled society women in furs with Louis Vutton bags swimming down the pipe. I may never be able to boil crab again! JK.]

                            1. re: kaleokahu

                              LOL. I have no idea what that says about my subconscious , but I don't like it.

                    2. re: cowboyardee

                      "I don't think you are correct here."

                      I didn't notice a temperature drop off at dead center in my tests, no. But that was on low heat. On high heat, my burners flare out more, leaving a larger gap in the center without direct flame. I can definitely notice a cooler spot in the center with my thermometer, though it's most prominent in the early stages of heating. As cool as the edges? Of course not -- but it's definitely there. And my burner is not large. A very wide burner would definitely create a ring effect.

                      To take an extreme example, imagine a giant pan many feet in diameter and a giant ring burner that was perhaps a couple fewer feet in diameter. The cold spot in the middle will probably be quite significant, even though the curvature around the center will tend to conduct more heat in that direction.

                      The question, of course, is where between the extremes of a tiny burner and an enormous impractical burner does the ring effect become significant? For pans with low conductivity, I think it can happen even on a standard kitchen range and definitely on a very wide burner.

                      I posted this link in a reply below previously, but I think the photos here show that the situation I'm describing is definitely possible (though it mainly appears in this link on induction rather than gas). Induction targets the ring more clearly, of course.


                      1. re: athanasius

                        I'm not sure we're understanding each other.

                        First off, the professional-style, wide ring burners I'm talking about are actually a little different from standard smaller home models - on high heat the pro models don't create a larger ring. The size of the ring is constant, and turning the knob only makes it more or less intense. I'm talking about a wide ring of flames directed more or less upward rather than a small ring of flames directed outward as a home model is. Does that clear up some confusion?

                        Second, I'm not claiming that a wider ring would eliminate all heat differences in the pan - just that it would minimize them. That a pan heated by a small centralized ring would have larger heat variances than the same pan heated by a ring that extended nearly to the edges of the pan.

                        Heating the pan on high heat created this effect inadvertently - on high heat, the heat is applied mainly to the edges of the pan. Try this - instead of making a point of getting the pan up to 700, take note of temperature differences of a pan heated on high heat (wide ring heat source) once it got to 300-400. I bet you don't see the 200 degree temp differences you saw when heating to the same point on low heat - which is counterintuitive because you actually gave the pan less time to diffuse heat and even out.

                        Finally - in your example, of course there will be a cold spot in the center. My point is that the cold spot will not be as drastic as you might think. And even more so, that cold spot will not be anywhere near as drastic as if you took that same huge pan, many feet in diameter, heated it with a centralized ring proportional in size to that of your burner on low heat, and then measured the temperature at and near the edges of that huge pan.

                        My point isn't that there is no 'ring effect.' It's that the 'ring effect' is less drastic than the 'small centralized burner effect.'

                        1. re: cowboyardee

                          "My point isn't that there is no 'ring effect.' It's that the 'ring effect' is less drastic than the 'small centralized burner effect.'"

                          I guess we don't disagree at all, then. If you read my previous posts, I never said the effect was large. All I claimed was that there was an effect, and it would become greater with a larger ring burner. Thus, there is a limit to how much you could potentially even out the heating on cast iron by making the burner wider. That's all I was saying.

                          "I'm talking about a wide ring of flames directed more or less upward rather than a small ring of flames directed outward as a home model is."

                          I know how professional burners work. I was just explaining why I didn't see the effect on my home burner in the tests at home, but I do see it at home in the tests on high.

                          "Try this - instead of making a point of getting the pan up to 700, take note of temperature differences of a pan heated on high heat (wide ring heat source) once it got to 300-400."

                          I believe that's exactly what I reported in my original post -- see above: "Over high heat, the temperature differential was slightly better at first, I think because the burner flares out more on high heat. But it still was always greater than 100 degrees different across the bottom of the pan. And once the center got above 500F or so, I started seeing 150-200 degree differences again for the edges...."

                          I understand exactly what you're talking about here. I'm just saying that unless you're heating evenly across the whole pan, you're not going to get even heat distribution. A wider burner helps, but only to some extent -- with a material with poor conductivity, there will be a cold spot in the center.

                          And by the way, I never claimed the cold center spot would be anything like the 100-200 degree difference. I said it was similar in magnitude to the other random hot/cold spots in the pan, i.e., could be roughly 50 degrees off.

                          1. re: athanasius

                            We really don't disagree. Initially I was just responding to this statement:

                            "Actually, on second thought, I don't know if a larger burner solves the problem, at least on a typical gas stove."

                            ...which is true. It doesn't solve the problem. I just wanted to point out that it lessens the problem. A little bit. Assuming you have pans of the right size. A lot of work for such a small point.

                            The only thing I still disagree with (and again, only slightly) is this line:

                            "I'm just saying that unless you're heating evenly across the whole pan, you're not going to get even heat distribution."

                            I stated my case about this statement in response to Kaleokahu directly above.

                            BTW, I never intended this as criticism of your experiment at all, as it has little to do with the actual specific properties of cast iron versus other mediums. Just a tangent that I find interesting.

                            1. re: cowboyardee

                              Oh, of course I didn't think of your response as a criticism. And I agree, it's an interesting related discussion, which I hadn't much thought about until Caroline brought up the burner size issue.

                      2. re: cowboyardee

                        It does make sense. It's obvious from the geometry, in fact. The heat capacity is proportional to the volume of metal to be heated, and the heat loss due to radiation is proportional to the surface area.

                      3. re: athanasius

                        With regard to heat delivery by typical American consumer grade gas stoves, I have observed the same cold spot in the center. The temperature distribution studies done with parchment paper or flour are interesting, however, both of these materials are very low mass and require very little heat transfer to reach their final temperature.

                        In a real life application such as browning a steak, significant heat transfer is required so there is value in another method of displaying temperature distribution while the pan is actually cooking something.

                        Specifically, I put about half an inch of water in a frying pan to determine the evenness of heat transfer. On the gas stove I tried, there was a ring of bubbles and the center was not boiling. I think that's pretty revealing.

                        1. re: pngai

                          Someone made video of the cold spot in typical gas stoves.


                          1. re: pngai

                            Hi. pngai:

                            My parchment scorchprints were made by placing the parchment and then filling the pan with glass beads.


                            1. re: kaleokahu

                              I was wondering how you kept the paper flat and in contact with the pan.
                              Do you feel the heat load of the glass beads is similar to what a steak would present?

                              1. re: pngai

                                Hi, pngai:

                                I honestly don't know. I just wanted to run a fair test with "food" in the pan.


                                1. re: kaleokahu

                                  That's my point. Given what we know about the high specific heat of water (which comprises a significant percentage of most foods like steak), I would think glass beads are much easier to heat up than real food.

                                  One analogy is to motors. If you want to measure the horsepower of a motor, you measure the RPM under load. Measuring the no-load RPM doesn't tell you much.

                                  1. re: pngai

                                    Why don't you do a "steakprint"? Flop a big 35-oz Porterhouse in your pan, leave it there for awhile, and see if there's a pattern when you take it out.

                                    1. re: kaleokahu

                                      As I have described, I did a boiling bubbles pattern with water and it showed what I expected: a cold spot with a typical gas stove.

                                      1. re: pngai

                                        Hi, pngai:

                                        Well, that method has its own problems, doesn't it? All that is showing is the difference between the region(s) of bubble formation and nearly so. Good for seeing the shape of the coil or flame, but the water is all within about 2F (so much for the cold spot), and the thermal mass of the water itself, the heat being evened by convection, is going to make the pan appear to be more even than it would be with solid or viscous food in it.

                                        Since you didn't like my steakprint suggestion, try "meatball-printing". My prediction is that you won't find an undercooked ball languishing in the center of your pan, but you *may* (depending on the size and construction of the pan) find balls lagging at the periphery.

                                        Would that be realistic enough of a test for you?


                                        1. re: kaleokahu

                                          The boiling pattern represents the heat transfer distribution which I consider the most important characteristic of the burner/pan system.

                                          But I disagree it makes the pan appear to be more even than it really is. Going back to the analogy of measuring motor power, two motors may have the same unloaded RPM but very different RPM under the same load if they are producing different horsepower.

                                          Another analogy is to volts and amperes. Temperature is like volts and heat transfer is like amps.

                                          Still another analogy is water pressure and flow (gallons per minute).

                                          Based on my measurements, I bought an induction cooktop. So I have no way to do these gas tests.

                                          Anyway, I just wanted to suggest you consider heat transfer and it's clear now that you don't seem to put much value in measuring heat transfer so I don't mind stopping here if you want.

                                          1. re: pngai

                                            The bubble test is more a test of the heat source than the pan. It shows where the pan is hottest, which will always be over the flame, the induction coil, or resistance heat source. In a poorly conducting pan that 'ring' will be more defined. If a pan conducts very well, a cool center spot might disappear.

                                            The scorch test complements that. It too depends on how the heat is applied, but it is also demonstrates how well the heat travels laterally in the pan. Neither test is going exactly mimic the conditions for a particular food. But a burner & pan that does well in both, will do well in almost all cooking conditions.

                                            Today I made pancakes. I used a carbon steel crepe pan on an coil burner, and cast aluminum pan on the induction burner. The browning pattern was equally uniform for a single 6" pancake. There was no evidence of a center cold spot on the induction burner (though that clearly shows in the bubble test). I had to switch the induction burner back and forth between 2 and 3 to keep the pan at the correct temperature, where as with the coil I know exactly where to set the dial.

                                            Indirectly, I also did a scorch test on the induction burner. I keep a paper towel on the burner to ease cleanup. With long term cooking like this (with temperatures in the 300-400F range), that paper slowly scorches. That pattern is a ring.

                                            1. re: paulj

                                              Hi, Paul:

                                              You said it better than I could, thanks.


                                              1. re: paulj

                                                Cast aluminum on an induction burner? Ohhhh... I see from your profile you live in south east Asia. Do you have an all metal induction stove or do you use an interface disk? If you've already covered this, sorry, I either forgot or missed it altogether. If you have all metal induction, I am SOOOOOOOO jealous! '-)

                                                1. re: Caroline1

                                                  SEA? Seattle (airport code).

                                                  As for the induction pans, I mostly have Berndes brand (or other similar European brands), both in stainless steel and cast aluminum. The aluminum pans have steel insert in the base. All bought at TJMaxx. Burner: Max Burton 6000.

                                                  1. re: paulj

                                                    LOL! When I read cast aluminum on induction, checked your profile and saw SEA (I know it's the Seattle airport code) the ONLY place that has all metal induction is Japan and (I think) Korea... SEA just had to be south east Asia if you can cook on induction with a cast aluminum pan. SO MUCH FOR INDUCTIVE LOGIC!!! '-)

                                                    Sorry 'bout that.

                                              2. re: pngai

                                                Hi, pngai: "...I disagree it makes the pan appear to be more even than it really is."

                                                I think you missed my meaning. If we hypothesize a really terribly-nonconductive pan (plutonium comes to mind), whose best is a small hotspot, fill it with water and bring it to a boil, the pan will appear more or less even in heat. Your telltale bubbles may emanate from a spot or ring, but the water will effectively be the same temperature. And if all we're doing is boiling water, the hot water will convect so that everything that is in contact with it (pan walls, water surface) is also effectively 210F.

                                                As Paul has pointed out considering heat transfer has as many variants as the foods we want to cook. I just think boiling water isn't a good approximation of "food" in general. But I agree with you that a completely empty pan is not a particularly good measure, either.


                            2. re: Caroline1

                              My 5 quart cast-iron surprised me when I preheated it 15 minutes or more on a gas cook-top and pointed my infrared thermometer at a whole lot of random points at a whole lot of random distances. I got readings from 450 (or even less) to 700 (or even more).

                              1. re: mrnelso

                                Yup, the "even heating" of cast iron has been a cynical lie all along.

                            3. Thank you for conducting this test! Very informative. I fell for the cast iron "even heat distribution" myth for years. Many TV chefs still perpetuate it! That and the "searing the meat keeps the juices in" myth.

                              1. Let us know if you repeat the tests with SS and clad pans. SS is even a worse conductor than CI (so I can guess how it will turn out, at least for monolithic SS), but its relative thinness might make for some interesting data.

                                The really cool thing about what you did is that anyone with an infared gun can replicate the tests on their own hobs and see for themself. Thanks!

                                1. Really people, put away the IR thermometers and get a life, (and get cooking.)

                                  You're not supposed to heat a cast iron anything by heating just the middle. You can only get even temps by heating the perimeter. You have to use the burner size that best matches the skillet.

                                  Also, last time I checked, the skillet has a handle (sometimes two). You will not be assessed a penalty lap if you pick up the skillet and move it around a bit. Builds strong muscles, too!

                                  Stirring is a useful technique. Also good for building arm muscle.

                                  Temps tend to even out anyway once you put food in (nothing much is accomplished in the kitchen by heating empty pots and pans) -- even a little cooking oil does wonders to even things out.

                                  For stuff that is really, really sensitive to temperature variations, by all means, go directly to copper. For most anything else, cast iron is OK.

                                  14 Replies
                                  1. re: MikeB3542

                                    "Stirring is a useful technique"

                                    No kidding. (agree).

                                    1. re: MikeB3542


                                      With respect, the OP was all about exploding the myth of cast iron being a good conductor of even heat. If that explosion was no news to YOU, good on you.

                                      That OP'r had spent a lot of frustrating time trying--and failing--to get even-heat results with cast. If you actually read the whole thread, you'll see heating the perimeter, moving the pan, clocking the pan, etc., seem not to help vary the results much.

                                      Doubtless, others have had the same experience and thought they were doing something wrong. The data provided, thanks to the OP and his/her infared thermometer, show they probably weren't, and will actually help "get a life" for some folks in the kitchen actually cooking.

                                      If strength training is what you're after, dig yourself an imu, tote some big rocks, split and pack some wood, build a fire, and bury your food til done. You don't need any metal at all for that. Complicates stirring, though.

                                      1. re: kaleokahu

                                        kaleokahu: "... exploding the myth of cast iron being a good conductor of even heat."

                                        So far as I am aware, no one who ever has used cast iron regards it as a good conductor, but most praise it for even heat BECAUSE it is a poor conductor. Generally the properties are not found in the same material.

                                        Cast iron is like an ocean liner, slow to turn, but hard to stop, while good conductors like silver are sports cars; the sports cars are quick, while the ocean liners have inertia. "Even heat" is just a euphemism for thermal inertia, which prevents cold ingredients thrown into the pan from creating cold spots locally.

                                        1. re: Politeness


                                          Despite appearances, I do not like to be contrary for the sake of contrariness.

                                          But yes, some people DO claim cast is a good conductor of even heat (which it is, in a weird way, compared with stainless steel). That they may conflate cast's overall poor conductivity with its thermal inertia is less important here than the import of athanasius' data. Those data tend to show that even heat is not something anyone is likely to get on a home gas stovetop with a cast iron pan or griddle.

                                          I'm not even sure the "thermal inertia" explanation of cast will survive the OP's IR thermometer. I know the conventional wisdom is that the cast pan holds heat better after a slow start and therefore doesn't go as cold as fast as other materials. And I know from my own experience that is true in finishing and resting food in the skillet off an active hob. But do you really think a preheated, thick copper- or aluminum-bottomed skillet is going to "go cold" on an active hob when a steak is flopped into the fat? Could it be that some of the oft-lamented "wasted" heat (stored in the gas spider or fading electrical coil) we debate in other threads might finish and rest the contents in Cu or Al skillets just as well as cast iron moved off the hob (or induction switched off)? Athanasius, get your gun!

                                          And no, even heat is NOT the euphemism for inertia you suggest. The OP proved that with his data that show <50F in temperature variation over the ENTIRE copper pan, all the way up the rim, whereas cast exhibited >200F variations just in the pan's BOTTOM. To adapt your analogy, the nimble sports car delivered far more even heat than the inertial ocean liner.

                                          I think cast pans' greatest cooking virtue--last soldier standing at >600F for searing--leads people to think cast has more practical inertia than it does. I mean, all other things being equal, if a thick, copper-disc-bottomed clad pan could survive the same high temperatures, how much more heat do you think a cast pan will "hold"? In other words, I think it's tempting to overestimate cast's heat-holding advantage when cast is the only skillet that starts the voyage at very high temperatures.

                                          1. re: Politeness

                                            "'Even heat' is just a euphemism for thermal inertia, which prevents cold ingredients thrown into the pan from creating cold spots locally."

                                            This is just my view, but to me, "even heat" means no local hot/cold spots, but cast iron definitely tends to form hot and cold spots. "Thermal inertia," also known as thermal effusivity in technical terms, is related. Even heating is a result of good thermal conductivity, while thermal inertia is a result of good conductivity and high heat capacity. Cast iron has a decent heat capacity with a relatively low conductivity (compared to copper, etc.), which means it has a mediocre thermal inertia. (In order to prevent cold spots from forming, you need heat to flow quickly through the pan; given cast iron's low conductivity, it will take longer for cold spots to heat up again.)

                                            I suspect you don't mean the technical definition of "thermal inertia," but rather something more like low thermal conductivity. That will prevent your pan's temperature from changing quickly overall, but it won't prevent hot/cold spots.

                                            I have in fact heard many people make claims that cast iron "heats evenly" when properly handled (preheated well, etc.). I'm pretty sure such claims have to do with *heating* the food, not whether the pan cools when adding new ingredients.

                                            In any case, cast iron isn't really the best choice for heat retention anyhow, since it has high thermal diffusivity and emissivity compared to, say, stainless steel, which means it tends to lose heat to the environment through conduction and radiation. See, for example, this comparison of two pots of boiling water (cast iron and stainless) left to sit -- the stainless performs much better at retaining heat:


                                            If you want something that retains a lot of heat and conducts really slowly, stainless is a good choice. If you want something that conducts heat well and avoids hot/cold spots, copper or aluminum are good choices.

                                            I think there's still an argument for searing with cast iron, though -- mainly because the lower diffusivity compared to copper/aluminum means that all the heat is not instantly transferred to food dropped in the pan, but rather leaks in a little more slowly. At superhot temperatures where copper would tend to instantly burn food through high conductivity and diffusivity, cast iron allows a slightly slower transfer. You therefore get something closer to the grilling/broiling experience in a pan, where the surface of the food is exposed to very high temperatures, but doesn't burn immediately.

                                            I'm speculating a bit here, though. My materials science is a bit rusty.

                                            1. re: Politeness

                                              As copper has significantly higher specific heat than cast iron, even with its superior conductivity, I wouldn't expect much in the way of cold spots from it.

                                              Aluminum, maybe. From first hand experience, I find this can sort of happen with aluminum at extremely high heat. At more moderate heat, it's not much of an issue. The presence of oil in the pan also helps (at moderate heat), evening heat distribution by convection. But in practical usage, i don't find this to be a major upside of cast iron.

                                          2. re: MikeB3542

                                            MikeB -

                                            I don't disagree with most of what you said, but I'll bite:

                                            "You can only get even temps by heating the perimeter."

                                            True for cast iron, not really necessary for aluminum or copper, as I tried to show.

                                            "You have to use the burner size that best matches the skillet."

                                            Won't work by itself for gas burners -- see my comment above. Larger burners just mean you get cold spots both in the middle and on the edges. Will work okay for electric/coils.

                                            "You will not be assessed a penalty lap if you pick up the skillet and move it around a bit.... Stirring is a useful technique."

                                            Yep, I get that. Sometimes I like to cook with more than one pan at once, though. That's a useful technique too, used for preparing more complex dishes.

                                            "Temps tend to even out anyway once you put food in"

                                            Sort of. I've been cooking in cast iron for years, and unless there's liquid in the pan, I still see significant temperature differences with food in the pan.

                                            "(nothing much is accomplished in the kitchen by heating empty pots and pans)"

                                            Except preheating -- also a useful technique. Last time I checked, lots of cast iron aficionados are big on the preheating, claiming that it leads to even heating. That's the primary myth I think my measurements debunk.

                                            "For most anything else, cast iron is OK."

                                            Sure, it's "OK." Usually I'd prefer a pan (or any kitchen utensil) that's more than "OK" if I have one. I like tools that are actually good for a particular job. And cast iron is good for some jobs. But I would argue its heat conductivity makes it a less than ideal choice for most stovetop cooking.

                                            1. re: athanasius

                                              This morning's discussion spurred me to do a little checking. For lunch today I made my very old, very reliable, very standard chicken teriyaki. Marinade boneless well pierced chicken thighs in a mixture of 3 parts shoyu, one part mirin, one part sake, and one part fresh ginger juice for twenty minutes to a half hour, then shake off liquid and add thighs skin down to a peanut oil filmed blistering hot cast iron skillet. I use a 12 inch skillet for six thighs. Brown skin side, turn and cover with lid until underside is browned, then turn back to skin side and add another part of mirin and equal amount of sugar to the marinade and pour over chicken and simmer/boil until sauce has reduced to a thick syrup that clings to the chicken thighs. Serve with rice. I've been making chicken teriyaki this way for decades, but it never before occurred to me to check the inner temperature of each thigh. Today I did. Using an instant read digital thermometer, to my great amazement I found the thighs ranged from a low of 163°F to a whopping 212°F at the high end. Fortunately, through the years no one has gotten sick from eating the lower temperature chicken, but in the future I do believe I will rotate the thighs in the pan while the sauce is reducing! What a surprise!

                                              1. re: Caroline1

                                                So how do you get juice out of a gingerroot?

                                                1. re: Sharuf

                                                  With my garlic press! '-)

                                                  I'm sneaky.

                                              2. re: athanasius

                                                I was trying to be provocative without stepping on too many toes -- the discussion is interesting if a little pedantic.

                                                As far as cast iron being "OK", my point of view is that cast iron performs remarkably well, especially when you consider the price. A single 12" Mauviel copper skillet will set you back $360 at Sur la Table. You could get EVERY available size and shape of skillet from Lodge for that. (A 12-0inch Lodge skillet lists at Sur la Table for $30, and they can be had for much less). And with a bit of patience and upkeep (I say that with tongue planted firmly in cheek!), the cast iron pan will be more stick-resistant than stainless or tin-lined copper, anodized aluminum, or stainless steel.

                                                1. re: MikeB3542

                                                  Mike: You're absolutely right about the acquisition costs of new copper vs. cast iron at full retail. If the choice was between one copper pan and the entire Lodge catalogue, that's not much of a choice.

                                                  Cast iron IS OK at most things--no aspersions or damning with faint praise at all. I don't think athanasius intended to disparage anyone who likes cast iron.

                                                  Pedantic or not, this discussion has at its core the news (to me anyway) that CI is not the even-heater it has been claimed to be. I am now--in 2010--closing in on completing a battery of copperware, all but one piece of which was gleaned from garage sales, Craigslist, eBay and friends. The total cost of all these pieces was substantially less than what I paid for fewer pieces of Le Creuset--in the 1980s--at retail. Had I known of the uneven heating data on cast iron revealed in this thread, that is money I would not have spent.

                                                  But hey, I LOVE my Lodge No. 12 camp oven, so have fun with what works for you.

                                                  1. re: MikeB3542

                                                    Mike -

                                                    "As far as cast iron being "OK", my point of view is that cast iron performs remarkably well, especially when you consider the price. A single 12" Mauviel copper skillet will set you back $360 at Sur la Table. You could get EVERY available size and shape of skillet from Lodge for that."

                                                    True. But notice that my other tested pan was an aluminum griddle with a non-stick coating, which I probably picked up for less than $20. I know some people are afraid of non-stick and/or aluminum, but if you're okay with aluminum in general, you have something in the price range of cast iron with significantly better performance.

                                              3. Athanasius,

                                                I never trust my cast iron pan as an even heat distributor -- simply based on my own experience. The folowing may be old news to you, but I figure I will put this link here.

                                                "The heavy copper and the light aluminum pans produced evenly toasted heat maps. The stainless-clad aluminum did pretty well, too. But the cast-iron pan scorched a small area, and the pattern was familiar.....When I spot-checked the cast iron with my thermometer, there was a consistent 100-degree difference between the pan center and an inch from the edge. That’s easily enough to make the difference between browning and scorching. "


                                                3 Replies
                                                1. re: Chemicalkinetics

                                                  Thanks so much for the link to the article - I love McGee, but I hadn't read this particular piece before. His findings don't surprise me, but it's good to know someone else (and someone with a reputation for using science in the kitchen) made similar observations.

                                                  1. re: Chemicalkinetics

                                                    By the way, here's a blog post I remember reading a while back that did a similar test to show heat patterns in cast iron versus aluminum:


                                                    The author here notes that small induction burners don't do well with aluminum, either. Since I don't have access to induction burners, I can't comment. But on my small-to-midsize gas burners, the copper and aluminum seemed to be pretty even. I certainly didn't see a disk-like hot spot in the aluminum or copper when running my tests the other day. Maybe such differences would be more visible on high heat, which I didn't focus on in the other pans.

                                                    Maybe I'll get around to trying a similar paper/flour experiment one of these days....

                                                    1. re: athanasius

                                                      Thanks for th link. It has very good visual demonstrations. The results from your own finding and on that blog do not shock me. Aluminum is definitely a better heat conductor than cast iron. I think the induction stove pictures are most interesting. The cast iron pan shows the true induction cooktop uneveniness. I am guessing the All Clad aluminum cookware mentioned here is the All Clad "stainless" cookware which is largely an aluminum pan. (you can see the specification on the webpage)


                                                      Because the way All Clad bonds their metals in the order of 18/0 exterior, thick aluminum core, 18/10 interior, it can distribute out some of the uneven induction power. Neverthless, the aluminum can only do so much. Clearly, a small stove is undesirable. Now, I do want to add that if the aluminum is omitted or if it is not placed in the middle of the 18/0 and 18/10 stainless steel layers, then the result will be closer to that of the cast iron, so it does make thing better.

                                                  2. Here's a thought regarding what to do about the uneven heating in cast iron. Perhaps it belongs in a new thread (mods?).

                                                    I can sense the widespread dismay and buyers' remorse that athansius' tests may cause in folks who care and who may have already invested heavily in cast iron over the years. Rather than throwing out the cast, buying an expensive new cooktop, or suffering with the unevenness, why not EVEN OUT the heat, spread and diffuse it with a layer of high-conductivity metal? I mean that's what the heavy multi-layer clad is supposed to do, correct? Granted, thick copper and aluminum pans already do that well, but the acquisition cost is relatively high.

                                                    So... why not buy one high-conductivity diffuser that can be used with--and help--any and ALL of your flat-bottomed cast iron pans? See, http://bellacopper.stores.yahoo.net/i.... At $35-$70, they're not inexpensive, but you'd be paying ONCE, instead of multiple times that for a new clad set or many multiples of that for monolithic copper. AND you can keep and better use your existing cast iron. These also seem to me to solve the griddle problem (and help with the "hob size" one), although they are not going to help push heat up a pan's sidewalls. Also good double-duty for force-thawing--saves water, ecos.

                                                    Just a[n] (politically incorrect) idea, food for thought.

                                                    Yes, there will be howls of derision at introducing yet more inefficiency--burn the coal to make the juice to heat the coil to heat the diffuser to heat the pan to cook your food... Yeah, I know, I'm just trying to help the folks cook better.

                                                    7 Replies
                                                    1. re: kaleokahu

                                                      This is an interesting suggestion -- I've thought of it myself in the past to get my cast iron working better, but haven't gotten around to buying a big slab of copper.

                                                      1. re: athanasius

                                                        I have a 1/2-inch-thick chunk of aluminum that is griddle-sized (a marine porthole or scupper cutout). It's large enough to straddle a couple burners. If I ever get a IR gun, maybe I'll play around with it under some cast pans. It works well just as a trivet and for defrosting.

                                                        I can't tell how thick those copper diffuser squares are in the link, but my guess is between .125 and .250 (Approx, 3mm to 7mm). A truly thick slab of Cu in the range of my porthole (free) is going to cost hundreds at retail.

                                                        1. re: kaleokahu

                                                          Actually, silver is a better thermal conductor than copper, and since you are going all out, don't scrimp on an IR gun, you can get a thermal immaging system, similar to the Army's night gogels and have a visual full color thermograph of the entire cooking surface. And for an additional small fee, I can set up the complete DOE and calculate the standard deviation for each experiment.


                                                          This entire episode should keep you not only pennyless, but off the streets for about 3 months.

                                                          1. re: mikie

                                                            LOL. No, not going all out, otherwise I'd be getting plutonium-sided, silver-bottomed saucepans to prevent the dreaded "waste" of energy into the room. Heck, I'm even trying to avoid shelling out $50 for a Chinese-made IR gun.

                                                            Actually, one $70 trivet purchase to solve the uneven heat problem with cast is quite a value. As would be a simple ferrous disc to solve the copper+induction problem.

                                                            Without basic experiments like the OP's and data to judge by, all we have is theoretical speculations and WAGs. Maybe I should get a life, but until I do, I'm eyeing getting that little truth-telling gun.

                                                            1. re: kaleokahu

                                                              "Without basic experiments like the OP's and data to judge by, all we have is theoretical speculations and WAGs."

                                                              I agree, and when I have more time on my hands (perhaps in a month or so), I might try out some of the things mentioned in the responses as further experiments.

                                                              I should also say that "theoretical speculations" could be quantified easily for someone willing to do the math. I took a heat transfer class years ago, and I've long since lost track of the textbook, but with some basic pan measurements and a bit of calculus, you could model at least the bottom of a pan pretty easily in terms of its thermal behavior.

                                                              In an ongoing joke, my heat transfer course began in the first lecture with the lecturer taking apart various coffee mugs for sale at the local college store. Subsequently, all of the exams consisted of modeling the behavior of a coffee mug under various circumstances and with various modifications to the coffee mug design. (The calculations were not easy, by the way.) We were all given coffee mugs at the final exam.

                                                              Anyhow -- for someone with the initiative and a bit of knowledge, it wouldn't be that hard to go from theoretical speculation to a reasonably accurate basic mathematical model. (For complicated pan geometries, like the curved surface of a saucier, though, you'd need to do computer modeling.) It would be surprising to me if food science journals hadn't done some of this sort of thing in the past.

                                                              1. re: athanasius

                                                                Your last reply is notable. Foremost because it is the first I've seen here on CH of a poster seriously proposing backing his/her theoretical speculations with a mathematical model. Good for you, I hope you remember more than I do from college, and teach us all some things synthetic even if they may be a priori.

                                                                But data and empiricism rule, as evidenced by your OP. So I hope there are experiments that follow to test the models.

                                                                Let me know if you are open to exploring related questions not necessarily involving cast iron.

                                                                Thanks again for your post--I learned.

                                                          2. re: kaleokahu

                                                            The vendor says the copper diffuser squares are all 1/8th inch thick.

                                                      2. Thank you for taking the time to test and document the results here.

                                                        I believe that some of the extreme heat differences (actually in all pans, but exacerbated and exaggerated by the low conductivity of cast iron) were due to your small burners, but I'll address that in another post above. I think you inadvertently demonstrated why professional-style wide gas burners are superior. (I'm curious how the pan would respond if you were to preheat cast iron on a small burner on high up to say 500-550 or so in the center and then turn off the heat and let it cool to cooking temp before turning the heat back on - would this be more even? I think it might as you are in effect creating a larger more even-heating burner, AND giving conduction more time to do it's thing)

                                                        Mostly, I just wanted to provide this link - it's the most comprehensive write-up of thermal properties of different cookware materials that I've seen.

                                                        Given the figures listed in that link, I don't find your results as surprising as some might.

                                                        43 Replies
                                                        1. re: cowboyardee

                                                          Thanks for the kind words and the link -- I remember reading through that post a few years back myself. And by the way, I didn't find the overall trend of my results surprising, but the magnitude of the temperature differences was a bit surprising to me.

                                                          Also, I'm intrigued by your idea of preheating to very hot and letting it sit -- I've definitely noticed my cast iron pan slowly diffuse heat throughout itself under those conditions. Something not mentioned on your link is that conductivity actually varies as temperature of a material changes -- thermal conductivity actually goes down in iron as it heats up. That would imply that heat is actually flowing slightly faster in cooler portions of the pan, but they can't catch up while the burner is on.

                                                          Of course, once the burner is off, you're looking at a race between conductivity inside the pan versus diffusivity and emissivity (radiation) going out into the kitchen (and thus cooling the pan). I don't know which would win, but it's an interesting question.

                                                          1. re: athanasius

                                                            "Of course, once the burner is off, you're looking at a race between conductivity inside the pan versus diffusivity and emissivity (radiation) going out into the kitchen (and thus cooling the pan). I don't know which would win, but it's an interesting question."

                                                            I don't really have the expertise to say for sure, but I'd bet that even for cast iron, conductivity is faster than emissivity.

                                                            Also, with conductivity within the pan, the hot spots should cool quicker than the cool spots, right?

                                                            1. re: cowboyardee

                                                              "I don't really have the expertise to say for sure, but I'd bet that even for cast iron, conductivity is faster than emissivity."

                                                              At some level, yes, but the question is when exactly you'll get the desired level of evenness -- will it happen at 300F across the pan, or more like 150F? That's really the question, because eventually the pan will all end up the same temperature, namely room temperature. Also, emissivity only accounts for heat lost to radiation, but there's also conduction and convection effects pulling heat out into the air.

                                                              "Also, with conductivity within the pan, the hot spots should cool quicker than the cool spots, right?"

                                                              Yes and no. Conduction rate is dependent on temperature difference, so heat exchange between the pan and the air due to conduction will be faster in hot spots. Convection effects are also enhanced by temperature difference, and radiation is higher with higher temperature (it's only really important at very high cooking temperatures).

                                                              But then you have to consider the process within the pan. Conduction, as I mentioned in my previous post, will occur more slowly in hot sections of the pan. That means that while heat is flowing out of the pan quicker in these spots, internal heat within the pan will take longer to even out in these spots, rather than in (say) minor hot/cool spots within cooler sections of the pan.

                                                              Heat transfer is all a very complex process, so I don't think we can say off-hand at what temperature the pan will reach a relative internal thermal equilibrium once removed from the heat.... it is a call for further experimentation, though.

                                                              1. re: cowboyardee

                                                                By the way, while your scenario is interesting, I don't see a huge advantage over, say, preheating the cast iron pan up in the oven. (Other than maybe some energy savings, depending on the size of the oven.)

                                                                In an oven you're much more likely to get even heat across the pan, and you can pull it out at whatever temperature you like.

                                                                1. re: athanasius

                                                                  Whoa, whoa, whoa, whoa whoa! I want the solution to involve elaborate processes and Rube Goldberg machines. No simple solutions allowed. Oven heating - bah!

                                                                  Most of my posts throw practicality out the window by the first sentence or two.

                                                                  But to get back to practicality for a rare second - I must note that my scenario would be a far quicker way of creating an even [mostly] cooking surface than heating the pan in an oven. If it works in the first place.

                                                                  1. re: cowboyardee

                                                                    Your solution would undoubtedly work, as I said, because at some point the pan temperature will acquire whatever reasonable level of evenness you want. The question is how hot the pan will still be when that happens and whether that would still be at a useful cooking temperature for your purpose.

                                                                    Of course, the problem is what you do then -- you throw food in this relatively even pan, but now you might want to continue to heat the food. But when you turn the burner on, you get the unevenness to start again.

                                                                    In terms of completely impractical solutions, I think such a situation calls for a large pulse of heat thrown at the pan periodically from the burner. That would perhaps allow the heat to spread out a bit between pulses, rather than to "pool" in one part of the pan.

                                                                    I don't know whether that would actually work, though -- but again, it sounds like a fun experiment. Preheat over high, cool until relatively even, and then pulse the burner on high for, say, 10 seconds out of every minute or two. What would THAT do?

                                                                    1. re: cowboyardee

                                                                      I accidentally happened upon a quicker and more efficient solution to your question of even preheating on the stovetop --

                                                                      Yesterday I found that my cast iron skillet had some crud in the bottom before I wanted to use it, so I cleaned it up with some water. While I got most of the water out of the pan, a little pool of water was left near the center of the pan, and I just figured I'd burn it off while preheating.

                                                                      Then it dawned on me -- just for kicks, I measured the temperature in the pan as it preheated. As I expected, the water in the center of the pan would not allow the surface there to go above 212F until it had evaporated, while the rest of the pan around it continued heating past 300F.

                                                                      The little pool of water finally evaporated, and the center of the pan started doing a quick catch-up -- the whole pan leveled out around 375F. Of course, after that, the heat in the center started to go past the temperature near the sides.

                                                                      But if you're looking to get a relatively even pre-heated cast iron pan without a lot of fuss, try putting a small amount of water in the center of the pan while preheating. It will allow the edges to warm up while the center loses heat in heating and evaporating the water.

                                                                      Of course, this requires a level stove and a relatively level pan (or one with a low spot near the center), and you'll still have to deal with unevenness during cooking.

                                                                      1. re: athanasius

                                                                        *Slow Clap*

                                                                        Very clever solution. Impressive. I imagine different amounts of water (or adding it at different times during the preheat) might make it level out at different temperatures too.

                                                                        1. re: athanasius

                                                                          IIRC, I *think* you're using one of those zap-read surface temperature thermometers, right? *IF* that is the case, your reading of the heat of the center of the pan will be incorrect because your gun is measuring the surface of the water, which will only reach 212F if you are at sea level. Or are you using another type of instrument to measure surface temperature?

                                                                          1. re: Caroline1

                                                                            I am using an infrared gun, but it probably isn't measuring the surface of the water, since the water is pretty transparent. Infrared thermometers are measuring infrared light, which gets transmitted through a lot of things that visible light does. For example, if I point my thermometer at a window, I won't generally get an accurate reading of the surface of the window, but I also won't get an accurate reading of the object seen through the window either, because some infrared light is lost going through the window.

                                                                            Or, for another example, you have to be careful when trying to measure the sides of a shiny pan with an IR thermometer, because at the wrong angle, infrared light from the bottom of the pan can reflect off of the side and into the thermometer -- so even if you point the thermometer at the side of the pan at certain angles, you might get something close to the temperature of the bottom of the pan.

                                                                            Anyhow, all of this isn't that relevant to the question at hand, since I'm talking about a thin film of water -- so thin that it doesn't flow across the pan, so the temperature at the top of that film will be roughly equal to the bottom.

                                                                            Moreover, we need to consider a certain basic thermodynamic fact -- if the surface of the pan underneath the water is hotter than 212F, any water in contact with that surface will instantly vaporize. Water cannot remain liquid next to a hotter surface (unless under pressure). If you have standing bubbles on the bottom of a pan of boiling water, the surface within those bubbles might be very slightly hotter than 212F, but probably not more than a degree or two.

                                                                            Finally, regardless of the readings of the water, the fact is that when the water disappeared, the pan underneath read approximately 212F and started to climb only thereafter.

                                                                            1. re: Caroline1

                                                                              The metal in contact with the water is also limited to 212F - unless the water is dancing around. Dancing water droplets (as when testing a pancake grill) move because there is an insulating layer of steam between the water and the hot pan surface.

                                                                              1. re: paulj

                                                                                <sigh> noooooo... If what you say is true, boiling water would levitate right out of the pan. The droplets skip because the hot pan burns their toes!

                                                                                But seriously, the amount of water athanasius is talking about in the bottom of a thick cast iron skillet cannot absorb enough heat to keep the pan's surface at 212F. 212F may be an atom or so deep, but it ain't all the way...! '-)

                                                                                1. re: Caroline1

                                                                                  "But seriously, the amount of water athanasius is talking about in the bottom of a thick cast iron skillet cannot absorb enough heat to keep the pan's surface at 212F."

                                                                                  I think you're underestimating the amount of heat it takes to evaporate water.

                                                                                  Heat capacity of water - 1 calorie/gram-degree Celsius
                                                                                  Heat capacity of cast iron - 0.11 cal/g-C

                                                                                  In other words, water requires about 9 times as much heat to raise its temperature as cast iron does.

                                                                                  but also:

                                                                                  Heat of vaporization of water - 539 cal/g

                                                                                  In other words, it takes about 7 times as much energy to evaporate water as it does to raise it to its boiling point from room temperature. That's why you can leave a boiling pot of pasta water on the stove cooking for quite a while, and the water level will only drop a little -- it takes a lot more energy to evaporate that water.

                                                                                  I had a puddle of roughly 1/8 cup of water in my pan, which is about 30 mL = 30 g. To evaporate that water, you need to raise the temperature by roughly 75 degrees C and then evaporate it:

                                                                                  30 g * 75 C * 1 cal/g-C + 30 g * 539 cal/g = 18420 calories

                                                                                  My cast iron skillet weighs roughly 1700 grams. To raise it to 100 C, you'd need:

                                                                                  1700 g * 75 C * 0.11 cal/g-C = 14025 calories

                                                                                  In other words, it will take more heat energy to heat that small puddle of water to boiling and then evaporate it completely than it takes to heat the entire skillet to the temperature of boiling water.

                                                                                  Of course, the water only strongly affects the cast iron area directly under it, which is less than 1/10 of the total pan weight. So, the water can definitely absorb enough heat to keep that area at 212F while the rest of the pan rises above 300F.

                                                                                  "212F may be an atom or so deep, but it ain't all the way...! '-)"

                                                                                  I never claimed that the bottom surface of pan (against the flame) was 212F. But most of the heat in the center of the pan will be sucked up evaporating the water.

                                                                                  1. re: athanasius

                                                                                    "Heat of vaporization of water - 539 cal/g"

                                                                                    That is the real important part.

                                                                                    1. re: Chemicalkinetics

                                                                                      Yep, perhaps this chart is useful for visualizing it:


                                                                                      Here, heat is added at a constant rate to go from ice cube to water to vapor. Notice how long (relatively) the water sits at its boiling point absorbing heat before evaporating.

                                                                                      1. re: athanasius

                                                                                        Nice. Thanks. I think that is a very nice diagram.

                                                                                        Similar information was also used to explain to me why steam is so dangerous. When hot steam hits a person, it is more than just the fact that it is >100oC. It is also the fact that steam packs a lot of phrase transition energy. When steam hits a person skin, the steam will start to condense and the skin temperature starts to rise -- energy transfer. However, there is just so much phrase transition energy between the 100oC steam to 100oC water.

                                                                              2. re: Caroline1

                                                                                Forget what I said about transparency -- I forgot how low the transmittance of water gets in the IR frequency range. So yes, you're right -- you would be measuring something close to the surface temperature of the water. But my other points still hold.

                                                                                1. re: athanasius

                                                                                  Okay, well here is a little test for you to try out for me because I don't have an infrared gun and there are too many things on the wish list ahead of it to wait until I get one, soooooooo... Take a pan that is much larger than your cast iron skillet, but that you can set the cast iron skillet in without problems with the handle hanging things up. Maybe a large cake pan or roast pan would work? Put two or three inches of water in the larger pan, then put something in the water for the cast iron pan to sit on that 1. doesn't have much "heat sucking" contact with the cast iron, and 2. prevents direct contact between the cast iron and the larger container with the water in it (not even the handle touching the edge of the pan) and 3. will ensure at least an inch or so of water between the bottom of the cast iron pan and the larger pan containing it. Bring the water to a boil, reduce to a shaky simmer, allow the cast iron to sit in the water bath empty for five or ten minutes to allow heat to distribute as evenly as possible. NOW zap the surface temperature of the pan in several locations. It might be interesting to do that immediately upon water boiling, then every minute or so afterward until you reach ten or fifteen -- even twenty? -- minutes. The thing I'm curious about and that this test should determine is whether cast iron is uniform enough in the fabrication process to promote even heating when placed in even heat. Or does cast iron have "rich spots" and "poor spots" where heat is compromised one way or the other? Is that an inherent quality of cast iron?

                                                                                  It would be really really good if you could do this, and I'm sure I would not be the only one who would be grateful...! Thanks bunches!!! :-)

                                                                                  1. re: Caroline1

                                                                                    I'll try to have a go at this one sometime, but I can predict the result -- the pan surface temperature should be pretty even.

                                                                                    A water bath will provide much more uniform heat than most other heat sources for cooking. Hot spots and cold spots in pans mostly tend to manifest themselves when you're trying to get heat to travel a long distance through metal -- for example, from near the center at a burner all the way to the edge of a large skillet.

                                                                                    If you provide a perfectly even heat underneath the entire pan, heat only needs to flow through the thickness of the pan from the heat source to the cooking surface, which is a much smaller distance. Even if the metal had pretty serious flaws, you probably wouldn't see major hot/cold spots under those conditions. (Also, we couldn't get a temperature greater than 212F under these conditions, not even 150F above room temperature -- if we had the pan at 600F or something, the dispersal of heat to air above the pan surface might be fast enough to see hot/cold spots more strongly.)

                                                                                    In any case, I'm not sure a test on one cast iron skillet could prove anything. I think iron can certainly be sand-casted in such a way as to promote a reasonably even crystalline structure on the atomic level, and machined to an even thickness, etc., which would give you even heating over an even heat source. The question is whether the process used by Lodge, Wagner, Griswold, etc. does this well and whether the process (which has changed a little over time) is consistent in skillets of varying age and make. Another issue is whether cooking temperatures could in any way affect the conductivity properties over time. Warping and other effects from high heat can certainly affect other materials, but I don't know how much it could affect cast iron over many years of use.

                                                                                    In sum, I think most cast iron pans would perform pretty well in your test, but that doesn't mean they'll perform well over most standard cooking sources. And even if my cast iron pan doesn't have hot spots, I'm not sure it would say anything about cast iron in general.

                                                                                    That said, it sounds like a fun experiment... :)

                                                                                    1. re: athanasius

                                                                                      hmmmmm... I have no idea why this thread didn't indicate your response in my "My Threads" page. I figured you must not be interested. Sorry about the late response but I just discovered yours!.

                                                                                      Yes, I'm aware of all of the stuff you talk about, but having a suspicious mind, frankly I just don't trust "tradition" all that much for precise knowledge. Our ancestors cooked in cast iron for millennia because it was the best they had. Doesn't mean it's the best in today's world, even through I quickly confess I am a STRONG endorser of the Century Rule: If it wasn't made or grown or used that way a century ago, CAVEAT EMPTOR! And maybe I'll be better off without it? I feel fairly confident that cast iron's reputation for even heating came about well over a century ago. And to my way of thinking, it might be true today if we cooked the way they did. I remember way back when I was a toddler, my great grandmother slid the cast iron cover off the "burner" of her wood fired stove and set a cast iron skillet directly over the opening to the blazing hot fire below. Maybe with that method cast iron would heat a lot more evenly than today's kitchen cooking methods heat it.

                                                                                      And yes, I'm fully aware that you can't get water to go over 212F without sealing it away by one means or another from the open atmosphere. Initially I suggested you do the experiment with cooking oil, then thought hey, synthetic motor oils will probably have a much higher smoke point than cooking oil, then I thought.... whoa, Nelly! I have NO idea what kind of safety precautions you can put into play, nor do I know if synthetic (or other high temperature withstanding motor oils) release toxic fumes as they're heated. After all, a crank case is cranked on pretty tight! So I decided to limit my suggestion to water and let you take it from there. And just for the record, if I wanted to suspend a cast iron skillet above another pans surface to allow fluids to circulate under it freely, I would go to a toy store and pick up a cheap set of jacks, then just use three or four of them. But far be it from me to tell you what to do...!

                                                                                      Do you (or does anyone else) know if motor oil releases noxious fumes when heated in open air? How hot can you take it before that happens? CURIOUS MINDS are standing around here stark naked waiting for knowledge to clothe ourselves...!!!

                                                                                      1. re: Caroline1

                                                                                        Wow... motor oil under my pan? I'm pretty sure the fumes would be problematic. (They're not too good for you even at room temperature.) Cooking oil would be possible, but as you said, it would require precautions.

                                                                                        You make a good point about the historical context of cast iron. I know cast iron cookware wasn't in use in Europe until after the year 1000, since they hadn't yet built furnaces that could attain the temperatures needed to melt iron. Old pots and cauldrons were made of brass or copper. When iron cookware became available, it was useful for its durability.

                                                                                        Modern stoves where you actually cook on top of them (as opposed to directly in/over the fire) came about a little before 1800. From a quick bit of research online, it seems at the time, cast iron cookware became very popular since it was easier to make it thinner (faster heating and response), and the pieces were often tinned to avoid the iron leaching into food. (Enameling was developed a little later.)

                                                                                        Perhaps someone else knows more about the history than I, but I would guess that the "even heating" idea of cast iron comes from its slow response, not from its lack of hot spots. If you had a cauldron of soup simmering over an open fire, it might be better to have a pot that wouldn't change temperature quickly when the fire died down a bit, or you threw another log on.

                                                                                        In that case, I think copper and other high-response materials could be a disadvantage, because they would require a very constant heat source for even cooking. That's easy with a modern stove, and it was okay with an old cast iron wood stove, which again evened the heat out for pots placed on top of it.

                                                                                        But before people cooked on top of stoves primarily, I'd imagine that cast iron would in fact have a reputation for "even heating." I still find it some of the best stuff for cooking over a fire when camping.

                                                                                        1. re: Caroline1

                                                                                          If you really want to know the answer to your last question?

                                                                                          My opinion is that yes moror oil releases noxious fumes when heated in open air. I'm not sure jsut exactly what hydrocarbons are released and at what temperature, but that is the refining process essentially. Drive behind an old care and decide for yourself if the fumes are noxious or not. The flash point for motor oil is around 220 to 240 °C (425 - 465 °F) so thats where the noxious fumes start. And that's the naked truth.

                                                                                          1. re: mikie

                                                                                            ummmm.... Mikie... Hello! By the time exhaust fumes escape from the tailpipe of a car, the MAJORITY of the fumes are from EXPLODED GASOLINE and NOT motor oil...! Which is why you don't have to refill your crank case as often as you have to refill your gas tank. Ideally, a crank case doesn't lose any oil, but in older cars with pretty much shot rings on the pistons, you can have motor oil reach the combustion chamber and burn and exhaust along with the gasoline.

                                                                                            So I repeat... I don't know at what temperature motor oil, especially synthetic motor oil which presumably has a higher flash point than petroleum motor oil, begins venting noxious fumes from being heated. *IF* synthetic oils vent less and at higher temps, and are only noxious and not toxic, than standard petroleum motor oil, and if a very safe OUTDOOR venue could be set up, then doing the experiment to check whether heat distribution in cast iron pans is uniform when the heat source is uniform would be an interesting experiment to perform.

                                                                                            Sometimes I think I should open another Chowhound account with a name like MachoMan or something. "Caroline1" seems to come with a lot of preconceived notions about whether or not I can think. Chauvinism lives! <sigh>

                                                                                              1. re: c oliver

                                                                                                It would certainly seem so. The point I've been trying to get across subtly since these discussions began is a simple one, so I may as well just come out and say it because subtlety is LOST...!!! You will NEVER get EVEN heat distribution across the bottom of ANY pan, regardless of what the pan is made of, UNTIL you find a means of applying EVEN heat to the bottom of the pan. Period. Therefore, when it comes to cookware, "practical heat conductivity" of ANY pan or pan material is irrelevant when the hobs, hot plates, burners only and exclusively deliver uneven heat from the get go. <sigh>

                                                                                                1. re: Caroline1

                                                                                                  Caroline: My IR thermometer and your flour photos are coming next week. I think your last post is generally true, but we will see what differences materials and thicknesses make.

                                                                                                  1. re: kaleokahu

                                                                                                    Go for it! '-) But my "prophesy" is that you will be putting in all of that work to produce identical heat distribution images of the hot spots produced by the BURNER as it is rendered by the different materials of the different pans. I do believe cooks have been stirring food for millennia simply because it will burn in the hot spots if they don't. Stirring is a practical method of gaining even heat distribution that pan heating methods do not deliver. It is NOT a fault of the pan, it is a fault of the burner/stove/fire. It doesn't matter whether you use a glass pan, a ceramic pan, an aluminum pan, a carbon steel pan, a copper pan, or sterling silver pan or any other kind of pan. The flaw is with the heat source.

                                                                                                      1. re: c oliver

                                                                                                        Sometimes I feel as if I'm in the midst of a group of rabis debating how many angels can dance on the head of a pin. What possible difference can that make to a seamstress?

                                                                                                      2. re: Caroline1

                                                                                                        If there's just a thin layer of food, you won't need to stir if the pan bottom is evenly heated. But usually stirring moves food up and down, so new parts come into contact with the hot bottom.

                                                                                                        1. re: paulj

                                                                                                          Paul, you seem like a nice enough guy, but when you make statements like, "If there's just a thin layer of food, you won't need to stir if the pan bottom is evenly heated" you are coming across as a VERY inexperienced cook! Not all foods and/or blends of food cook the same. Even heat will make no difference as to whether you have to stir if you are cooking something like a bechamel, or anything with fine particles in it that will settle to the bottom and scorch/burn if not stirred. When and why foods must be stirred is NOT exclusively an action that is required because of uneven heat under a pan. WHAT you are stirring is also critical.

                                                                                                          1. re: Caroline1

                                                                                                            When I read that comment last night, I thought of omelettes. Couldn't be much thinner but still has to be moved around quite a bit in the beginning.

                                                                                                            1. re: c oliver

                                                                                                              Traditional risotto is another dish that comes to mind. There are a lot of recipes that require constant stirring regardless of how even the heat source may be. I avoid having to stir with my magic device that runs on batteries and turns paddles against the bottom of the pot so I don't have to stir. Magic! Costs about thirty bucks. And they don't (to the best of my knowledge) make them any more. But I can make risotto or bechamel or scrambled eggs (but not an omelet) without doing the stirring myself! '-)

                                                                                                            2. re: Caroline1

                                                                                                              You misunderstood the point I was trying to make. I got the impression from your previous post that uneven heat was the main reason we stir food, so it won't stick where the heat is highest, etc. I was conceding the point that there may be cases where we don't need to stir, if the heat is even enough. But my main point was that stirring does more than compensate for uneven heat (across the pan surface) - it brings new food into contact with the bottom.

                                                                                                              A thin layer of diced onion with enough fat does not need much stirring if the heat is even enough. Crepes are another example.

                                                                                                          2. re: Caroline1

                                                                                                            Car: Yes, you are mostly right, as usual. If you remember the recent foodfight/pulldown over hot spots on induction, you will recall that this was pointed out: All other things being equal, a narrow single-ring burner (even induction) is more prone to giving hot spots than a heat source that heats the whole pan bottom. At least radiant and spiral resistive (and multi-ring gas) hobs do a decent job of covering the entire pan bottom.

                                                                                                            However, I do not think the "point of the flame" is quite ALL there is to it. Thickness and high conductivity metals have roles as well.

                                                                                                            We will see about your prophesy. I will also try to TIME the hot spots' appearance in the flour, for those of us who would like to stir a little less.

                                                                                                            Does this count as one of my 3 free passes?

                                                                                                            1. re: kaleokahu

                                                                                                              Well, because you're so charming and so willing to do the experiment, I'll just dock you one half of a free pass. '-)

                                                                                                              Fact: With all of the materials easily available to home AND professional cooks today in the varied and sundry forms of "cookware," NONE is capable of redistributing heat evenly throughout the cooking surface of any cooking vessel.

                                                                                                              Let's talk briefly about convection currents. The first thing home and professional cooks should understand is that "convection ovens" DO NOT cook by convection! Convection ovens cook by preheated forced air circulation. Standard old fashioned ovens cook by convection. Convection is the flow and eddy patterns that heat produces when passing through a liquid, solid, or gas while trying to find equilibrium. There is NO metal known to man, that I am aware of, in which heat will uniformly overcome the resistance offered by the molecules or elements of that material and attain even temperature throughout the metal, whatever form it is in. Use any material in a pan designed for cooking and the rules of convection do NOT fall away! Which is why, in the flour experiment, you will ONLY be able to display how each metal scorches flour due to the [uneven] heat distribution delivery system of the burner beneath it.

                                                                                                              HOWEVER....! More even heat sources CAN be produced for surface contact cooking. But in order to do that you must do something along the lines of what a "convection oven" does by forcing the air inside an oven to circulate rapidly overcoming and "stirring up" the natural flows and eddies that standard convection would produce inside the oven if the fan wasn't running.

                                                                                                              To accomplish something fairly similar with a cooking surface, the only way I can think of doing that and still maintain access to the food while it is cooking is with the method I have suggested to athanasius using a fluid "moderator" between the heat source and the cooking surface. In a convection oven, the food is not accessible for direct contact without opening the oven door, which immediately negates the benefit of forced air heat distribution, so obviously, you're not going to add new ingredients without interrupting the even heat. BUT...! If you put a layer of liquid that can handle high temperatures between the heat source and the cooking surface, then you can heat the liquid to the temperature that you desire and force constant circulation of the fluid that will "standardize" the cooking surface temperature using a method very similar to what happens when a fan breaks up natural convection patterns and forces uniform heat in an oven by using a fan.

                                                                                                              Can such a cooking surface be built? Yes. I believe it can. The easiest way to do it would be in the form of a "flat top grill" with a layer of thermostatically heated and circulated fluid in a sealed chamber under the "flat top" that uses the actual flat top as the upper surface of the chamber. Will this mean that the entire cooking surface of the flat top will stay uniform even when food is placed on it? No. There will be contact shock as there is any time a cold surface meets a hot one. BUT it WILL regain equilibrium MUCH faster than any other surface cooking method now available to us. You COULD use a pan on this type of device and gain even heat for the bottom of the pan, but you would have the same contact shock when foods are introduced and whether or not the pan will make "full body contact" will make a huge difference in whether the pan works with the same efficiency as the grill surface. Also you would still have to stir things that require ingredients to stay in suspension to avoid scorching or burning. But you could get some fantastically browned cottage fries!!! '-)

                                                                                                              Is any appliance manufacturer currently developing such a thing? I don't know, but I doubt it. It seems to be a characteristic of human kind to travel the same road over and over again forming ruts to guide the wheels of our vehicles OR our thinking. I hate it when that happens. <sigh>

                                                                                                              1. re: Caroline1

                                                                                                                Hi Caroline -

                                                                                                                For your fluid idea, it seems we need a substance with the following characteristics:

                                                                                                                (1) melting point below normal cooking temperatures
                                                                                                                (2) boiling point above normal cooking temperatures
                                                                                                                (3) able to be contained withing some sort of chamber of some reasonable pan material
                                                                                                                (4) preferably non-flammable and not explosive at normal cooking temperatures
                                                                                                                (5) preferably without serious health risks

                                                                                                                I somewhat jokingly suggested mercury as a material with many of the desired characteristics (except 5...) when you first brought up the "double-boiler" idea elsewhere on this thread.

                                                                                                                If we want to avoid health risks, what about gallium? It's solid at room temperature, but melts at body temperature, so it's liquid for standard cooking termperatures. The main issue with it, as far as know (and I don't claim to know much about gallium) is that it tends to dissolve many other metals, so you'd need to have a suitable container chamber.

                                                                                                                It seems to me that most oils and other organics are going to run into problems, either low flash point or some other chemical breakdown that will begin to occur if accidentally left on high heat. Then you'll have to take your pan out for an "oil change"....

                                                                                                                But perhaps someone here knows of another suitable material with the right properties.

                                                                                                    1. re: Caroline1

                                                                                                      Not intentionally trying to insult your intellegence, however, if you drive behind a new "non-oil burning" car you don't smell much, most of the byproducts of gasoline internal combustion engines end up being odorless, CO, CO2, H2O vapor, etc. However if you drive behind an old oil burnner, is really stinks.

                                                                                                      I provided a flash point for regular motor oil in my post above, so I'm not sure why you state you don't knowwhen it begins venting noxioius fumes, but here are some specific flash points for various brands and types of motor oils:

                                                                                                      Brand / Flash Point
                                                                                                      AMSOIL* 507
                                                                                                      AMSOIL Series 2000* 474
                                                                                                      Castrol GTX* 440
                                                                                                      Castrol Syntec Blend* 440
                                                                                                      Chevron Supreme* 428
                                                                                                      Exxon High Performance 419
                                                                                                      Havoline Formula 3 465
                                                                                                      Kendall GT-1 390
                                                                                                      Pennzoil GT Perf. 460
                                                                                                      Quaker State Perf.* 440
                                                                                                      Quaker State Motorcycle 440
                                                                                                      Red Line 503

                                                                                                      The list goes on and on, but I think this is sufficient to make the point, the most you are going to get is about 450 to 500 °F even for synthetic oils. The first and last are full synthetic motor oils.

                                                                                                      BTW, I don't disagree that an even heat source would provide a more evenly heated pan. For your experiment you need a heat transfer fluid. Might I suggest an "Open Bath Fluid" such as Duratherm S with a flash point of 615°F, this is a silicone heat transfer fluid. Hopefully you won't need to cook at temperatues higher than this.

                                                                                                      1. re: mikie

                                                                                                        Okay. First paragraph. Yes. It *IS* possible for a car to emit smelly fumes when it is not burning oil because of bad rings on one or more pistons. For years I drove Mercedes diesel cars exclusively, and they smelled bad when I wasn't burning oil from the crankcase. I'm not trying to split hairs, but you appear to have a tendency to make general statements that are only true when pared down to certain specifics.

                                                                                                        Now, looking over your list of motor oil flash points, and using YOUR definition that a "flash point" is the temperature AT or ABOVE which heated motor oils begin throwing off noxious fumes, then my ORIGINAL SUGGESTION that a motor oil could be used in an outdoor environment with safety precautions is valid. It would be a brief experiment, good results can be gained by not going above 400F, and it would determine whether the premise of an even method of delivering heat to a cooking vessel's bottom would bypass the uneven heating problems seen with standard stove, cook tops and hot plates on the market today.

                                                                                                        And finally, an evenly heated heat source would DEMAND a full contact cooking vessel with an even heat delivery surface and that is highly improbable, so cooking directly on an evenly heated flat top grill is a much better way to deliver optimum uniform cooking temperature to food. Pans warp. Many flex in and out of warp during heating. You can't escape nature, so it is much wiser to understand nature and meet her demands. If nothing else, it's a lot cheaper than trying to create new and unknown materials with the desired characteristics.

                                                                                                        1. re: Caroline1

                                                                                                          "For years I drove Mercedes diesel cars exclusively, and they smelled bad when I wasn't burning oil from the crankcase. I'm not trying to split hairs, but you appear to have a tendency to make general statements that are only true when pared down to certain specifics."

                                                                                                          I guess you didn't really read my post: " if you drive behind a new "non-oil burning" car you don't smell much, most of the byproducts of gasoline internal combustion engines end up being odorless, CO, CO2, H2O vapor, etc." I was very specific to use the word gasoline, to avoid the very diesel car theory that you mention. I just don't know how to get more specific than that without spelling out a 2010 Chevy Malibu with a 3.5 L normally asperated 4 stroke gasoline engine. I thougt that wouldn't be necessary.

                                                                                                          Flash point is not MY defination of anything, it's an industry available number that by defination is;
                                                                                                          1. The lowest temperature at which the vapor of a combustible liquid can be made to ignite momentarily in air.

                                                                                                        2. re: mikie

                                                                                                          This is really a post script to my last post above but I didn't want to add it as an edit in case you've already read that post.

                                                                                                          I have requested a price quote for 2 liters of Duratherm S and been notified it will take them 24 hours to respond. If you already know the price I will have to assume it is prohibitive and that safe means of using synthetic motor oil for sub 400F testing outdoors is the most practical solution.

                                                                                                          1. re: Caroline1

                                                                                                            I don't know the price, we use heat transfer fluids at work and I'll be shocked if they aren't more than 2 quarts of of Amsoil synthetic, which is pushing $10 a qt. I've never seen a temperature for motor oils for smoky "I don't want to be breathing this stuff", nasty crapola, if I had that temperature I would have freely provided it for you. The best I could find was flashpoint, it's what the industry uses. I think you will be safe at 400F, at least it isn't going to instantly burst into a flaming inferno. I do know a guy that had an oil fire under his hood when the oil that was leaking dripped on a hot exhaust manifold. How hot does a turkey fryer get anyway?

                                                                                                            The MOST important thing if you go forward with this is for God's sake, be carful! All this technical stuff is a lot of fun and certianly interesting, many of us have stayed up late looking up data to share, but we certianly don't want anyone to get hurt trying to prove a point. At work we have three common sense principles the first of which is Work Safely of Not At All. Just make sure you are safe.

                                                                                                            Good Luck!

                                                                                  2. re: athanasius

                                                                                    You're optimizing the wrong thing. The evenness of the temperature distribution of an empty pan is pointless. The objective is to cook food, so what matters is the evenness of the temperature distribution of a pan with food in it. The food will be at a lower temperature than the pan so the temperature distribution will be determined by how evenly the pan transfers heat.

                                                                                2. Well, looky here... The NYTimes tells me that the Nobel committee has awarded a big prize in physics to some guys who may have come up with the greatest material for cookware ever! Heat conducting unheard of... Maybe it won't be too expensive, but who knows? Anyway, it's phenomenal stuff in flake form only one atom thick and you can read about it at the link below. I've got an order all written up for a set of Graphene pots and pans. Now all I have to do is figure out where to send it!


                                                                                  5 Replies
                                                                                  1. re: Caroline1

                                                                                    Car: "Maybe it won't be too expensive..."

                                                                                    Um hmmmmm, sure. We can pay for it with the big bucks we'll save by using induction. BUT WAIT!!! It won't work with induction. Never mind...

                                                                                    But seriously, thanks for posting this. Interesting stuff.

                                                                                    1. re: kaleokahu

                                                                                      It is monolayer. Heat only conducts in 2-dimension (not 3-dimension). This is the same problem with graphite as well. Graphite has excellent thermal conductivity in one axis, but not the other two. Graphite is cheap too.

                                                                                      Here if you scroll to carbon graphite, you will see it has thermal conductivity of 1950 kW/m.K in one axis. Copper is only 401. However, graphite only has thermal conductivity of 5 in the other two axes, worse than stainless steel


                                                                                      This is why sometime ago, I said using diamond. Diamond has 895 in all directions.

                                                                                      P.S.: Slow conductivity in one axis is not bad if it is uniformaly slow.

                                                                                      1. re: Chemicalkinetics

                                                                                        Do you know where I can pick up some diamond pots and pans at a reasonable price? That should put some bling in my kitchen, and be absolutely stunning on my black granite counters! '-)

                                                                                        1. re: Caroline1

                                                                                          Don't know, but I figure that one diamond pan is probably all you ever need. It has high thermal conducivity, prestige, low electric conductivity. That's right. Unlike metal, diamond has great thermal conductivity, but poor electric conductivity, so you know you will never get electrocuted by holding a diamond pan. What a safe cookware! Oh yes, it is nontoxic unlike copper, so you will never have to tin it.

                                                                                          1. re: Chemicalkinetics

                                                                                            Well, that brings up the question of whether to go for the faceted look or en cabochon. But I've never seen a cabochon diamond. Maybe something about the lattice fights it, but I wouldn't think so. But hey, any way I can get it. Fry an egg without fat and see whether the bottom has browned before you turn it out of the pan. What could be better than that?

                                                                                            Still, wih those little graphene puppies, if you stack them all so they're impecably transferring heat bottom to top, who cares if heat goes sideways? Bring it on!

                                                                                  2. From a pure science stand point, I think your practical experiment confirmed what science has already established. Here is the thermal conductivity of variious metals measured at 500°K (~440°F) in Watt cm E-1 °K E-1

                                                                                    Aluminum 2.37
                                                                                    Copper 3.88
                                                                                    Iron 0.61

                                                                                    The higher the number the better the thermal conductivity, so copper is about 1.5 times better than aluminum and almost 6.5 times better than iron. What this tells you is, it's going to take a much longer time for the iron pan to move the heat from the source to the other parts of the pan, including the handel.

                                                                                    Without teaching a class in thermodynamics, the specific heat of the pot material and the mass of the pot and how much heat input you have will determine the temperature change.

                                                                                    1 Reply
                                                                                    1. re: mikie

                                                                                      Thanks, mikie. I completely agree. The reason I tried it though is because I've seen conductivity numbers posted all over the internet (and in previous threads here) about pans, but you still hear about the supposed "even heating" of cast iron.

                                                                                      As has been discussed in a few of the replies above, heat transfer is of course a rather complex process (it's been a few years since I took a course in it), and without empirical data, it's difficult to get a sense of how to sort out the practical effects of differences in conductivity (as well as specific heat, their combined effects in diffusivity, etc.).

                                                                                    2. Here's the issue I have with your test.

                                                                                      You turned the burner on low while in "real life" most of use would turn the burners to at least medium to medium high.

                                                                                      What you don't account for with thermal mass and cooling.

                                                                                      Would you see this great temperature difference if the burners were turned to medium to medium-high?

                                                                                      2 Replies
                                                                                      1. re: dave_c

                                                                                        "You turned the burner on low while in "real life" most of use would turn the burners to at least medium to medium high."

                                                                                        I did this because I was heating empty pans for a long time and didn't want to overheat anything (particularly the non-stick pan). I also have heard many cast iron fans say preheating on low or medium-low is the best route to even heat. Isn't that something people do in "real-life"?

                                                                                        "Would you see this great temperature difference if the burners were turned to medium to medium-high?"

                                                                                        I did address this: "I did brief trials over medium and high heat, but I didn't try to heat to equilibrium, because I don't like to preheat empty pans to over 400F except for searing purposes. In general, I observed similar patterns in terms of the differentials between center and sides at higher temperatures." etc.

                                                                                        No matter what the burner setting, I always see at LEAST a 100F temperature gradient across the cast iron. No matter what the burner setting, I see a 30F gradient or less across the bottom of copper. This is the result of the basic thermodynamic properties of the materials, as has been discussed in the posts above.

                                                                                        The low burner just shows that you can't claim these differences disappear over prolonged heating. The cast iron would just have a similar pattern, just a few hundred degrees hotter.

                                                                                        1. re: dave_c

                                                                                          If the heat input is increased, the temperature differences will be greater.

                                                                                        2. I've been waiting patiently for people to start posting photos of the results of their personal experiment a la the one athanasius posted. Well, to be specific, this one: http://www.cookingissues.com/2010/02/... I think that's a most elegant experiment! I mean, how many other experiments create their own graphics as the work progresses? So far, I don't see any pictures posted! What's wrong with you guys????

                                                                                          I've been thinking about this "male" quest for the perfect pan. And I put quotes around male because I think this is one area where women, for the most part, are a bit more pragmatic in their approach. However the pan behaves on the burner as far as heat transference is concerned, it's something that has to be dealt with to get a meal on the table so just get on with the cooking. I think it's a guy thing to obsess over cool spots. But hey, what am I doing here?

                                                                                          I have been thinking about this quest. I don't think it's probable that there is any way of getting evenly distributed heat in the bottom of a pan placed directly on a burner. On the other hand, there ARE pans that do deliver very even heat across their bottom. They are called "double boilers." The bottom of the interior pan that is cooked in is heated by steam in a closed chamber beneath it, and the heat transference is the maximum that is possible with whatever sort of metal the upper container of the double boiler is constructed of. I've seen double boilers of incredible variety! All aluminum top and bottom pans, all Pyrex glass top and bottom pans (which are kind of fun because you can watch the whole process), copper bottom with ceramic top, and all sorts of other variations.

                                                                                          Now, the problem with double boilers, as we know them, is that they do not produce heat high enough for frying or sauteing. But it does seem to me that a "sort" of double boiler could be made in which the liquid (presumed water, but there may be other liquids that are more suitable in this case) is sealed inside a pan where it can heat the cooking surface to higher temperatures than are attained in non-sealed standard double boilers. Real-life double boilers teach us that the water in the bottom pan cannot touch the bottom of the top pan, the heat to the top pan must come from steam. Would this still be true with a sealed bottom chamber that cannot interact with the atmosphere? Admittedly, this will take some extra study and experimentation. How can a liquid produce steam in a closed chamber? Would adding a lot of oxygen under pressure with water in a sealed chamber work by providing enough oxygen that will stay there until the seal is broken to allow "steam" to build in the chamber? It would probably also require a pretty special metal to withstand all of the interior pressure that would build. Will it need a petcock to keep from exploding? I don't know the answer to these questions, but I do have some thoughts on the probabilities. It needs a little work, but I think this is the most probable way of being able to come up with even heat distribution over a single cooking surface.

                                                                                          But maybe we're not supposed to have even cooking surfaces? Maybe that's why God gave us rotisseries? And of course, the BIG question is, "Will food cooked on a mono-temperature cooking surface taste better than food that is not? Somehow, I doubt that. I doubt it very much. I think the real art of cooking comes from what goes on IN the pan and not so much from what goes on under it! '-)

                                                                                          5 Replies
                                                                                          1. re: Caroline1

                                                                                            athanasius did post that link, which you also posted.

                                                                                            What male quest?! I don't care about much about hot and cold spots. That is why I still use a carbon steel wok and a cast iron skillet and have no desire to get the aluminum version, not to mention copper.

                                                                                            I think it is a woman thing.

                                                                                            1. re: Caroline1

                                                                                              Hi Caroline -

                                                                                              I can't speak for anyone else, but I'm personally not looking for perfection in my pans. I'm more interested in sorting out rumor from fact. A common rumor has it that cast iron, properly preheated, heats evenly. From the basic thermodynamic properties of the material, I doubted that, but on request from a few previous posts on another thread and out of curiosity one weekend afternoon, I decided to do a couple quick measurements to see what actually happens in my pans.

                                                                                              My personal experience tells me that I have less trouble getting better cooking results in other pans for many tasks. For a few, cast iron is good or even great. But I don't use it for all-purpose cookware anymore, not because I measured hot spots, but because I found other pans that make it easier to get better results in the food I'm cooking. All of this analysis is after-the-fact, for me anyway.

                                                                                              As for your theoretical high-temperature double-boiler, I think the quickest and easiest solution would be to seal in a pool of liquid mercury with some space for mercury vapor at roughly atmospheric pressure. Mercury's boiling point at atmospheric pressure is roughly 675F, so you won't build up any real pressure unless you go above that (which most cooking doesn't).

                                                                                              Bonus -- mercury tends to dissolve many metals, but iron is not one of them. So, you could put your mercury boiler chamber in the base of a cast iron pan, which would probably produce a very even heat pattern.

                                                                                              Of course... I don't think anyone's going to let you build such cookware, because mercury vapor is highly toxic, and if the chamber broke open, you'd have not only a health but environmental hazard. Nevertheless, if we're thinking in "manly" mode for the optimal heating surface, I don't think you could get much better than a double boiler over liquid mercury. :)

                                                                                              To be a little more serious, you could do something like this with an enclosed oil chamber, I suppose, since many oil boiling temps are high enough to make this work without high pressure. But many oils experience some sort of breakdown at high temperatures, so you'd have to choose your oil wisely. (Otherwise, you'd have to take your pans out periodically for an oil change -- talk about "manly"....)

                                                                                              In case you're actually wondering about the answers to your questions:

                                                                                              "...the heat to the top pan must come from steam. Would this still be true with a sealed bottom chamber that cannot interact with the atmosphere?"

                                                                                              The advantage of using a gas to transfer heat is that it introduces a tertiary barrier -- the bottom pan has hot spots, the liquid much less so, the gas much, much, much less so.

                                                                                              "How can a liquid produce steam in a closed chamber?"

                                                                                              Easy. You heat it above the liquid's boiling point at the pressure of the chamber.

                                                                                              "Would adding a lot of oxygen under pressure with water in a sealed chamber work by providing enough oxygen that will stay there until the seal is broken to allow "steam" to build in the chamber?"

                                                                                              I don't think you need pre-existing high pressure to get this to work. Heat the sealed container of water enough, and it will build its own pressure.

                                                                                              "It would probably also require a pretty special metal to withstand all of the interior pressure that would build. Will it need a petcock to keep from exploding?"

                                                                                              You'll need something to keep it from exploding, but any released pressure will lower the steam temperature. To maintain 450F steam, for example, you'd need about 30 times atmospheric pressure. For comparison, a pressure cooker isn't even twice atmospheric pressure, and look at all the safety features on those. Espresso makers also don't generally go over 10-15 times atmospheric pressure, and that's in a very small contained area. Those that have that high pressure produce the pressure by a pump, too, not by heating steam. 30 atmospheres is a typical rating for a big steam pipe -- to get 500-600F in your pan, you're not going to be able to do it by steam from water vapor.

                                                                                              Personally, I think the mercury double boiler would be much safer than a pan with steam pressures >30 atmospheres... but that's just me. :)

                                                                                              1. re: Caroline1

                                                                                                I think what you want is a pressure cooker/double boiler combination. Just about anything else is going to in some way defy the laws of physics. High pressure steam can get up to temperatures well above that of ordinary boiling water, however you might end up with a pot so solidly built you can't move it. 320 degree steam is not uncommon, but that's about the limit without super high pressure. The biggest problem you're going to have is the expansion and contraction of that liquid/oxygen space that you need to keep an even temperature in a sealed system. When you get the bugs worked out let us know. ;)

                                                                                                1. re: Caroline1

                                                                                                  Commercial and institutional kitchens such as school cafeterias have steam heated cauldrons. The ones I recall seeing (but not using) where about 3 ft across, about as deep with a rounded bottom, with a double wall (the steam jacket).

                                                                                                  Here are specs for a Cleveland electric steam jacketed kettle (up to 100 gallon size)
                                                                                                  In has a 50psi steam jacket rating, operating temperature from 145F to 260F

                                                                                                  1. re: paulj

                                                                                                    This is a good point -- I've seen these things, too, from afar. A quick Google search tells me many (most?) are rated to about 50 psi or ~3.5 atmospheres, which gets you to about 280F in steam under pressure.

                                                                                                    1. re: paulj

                                                                                                      Actually I was thinking of these guys:


                                                                                                      There actually is some cooking content in that video . . . .

                                                                                                      And these guys:


                                                                                                      "Put 50,000 (V) through it!"

                                                                                                      "Unfortunately that tends to carbonize the sausage"


                                                                                                      1. re: ZenSojourner

                                                                                                        "It's sad when engineers cook."

                                                                                                        I know you made this comment partly tongue-in-cheek, but I think it's useful to differentiate between three "engineering" approaches to cooking:

                                                                                                        (1) Science/engineering nerds playing around with food, often using crazy technology or methods. Your Youtube videos are examples of this.

                                                                                                        (2) Science/engineering nerds searching for optimum performance, the best gadgets, etc. to optimize stuff beyond the level that is useful in cooking. For example, I know a few people who keep their kitchen knives "scary sharp" -- why? Because they can. Is it useful for cooking? Not really. How useful is it to be able to slice through tomatoes in midair without any effort?

                                                                                                        (3) Scientists and engineers performing tests to study cooking techniques and improve technology/recipes, etc. Paul's site is an example of this.

                                                                                                        The first is for fun, the second is for hobbyists or obsessive types, but the last drives advances in cooking. Many cooks tend to think of what they do as an "art" that requires "talent"; in reality, the execution of a pre-existing recipe requires nothing more than consistent ingredients, standard equipment, knowledge of proper technique, and following directions. It really is chemistry in the kitchen. If that weren't true, master chefs could never delegate any food preparation in their kitchens to anyone else without compromising the results significantly. (This does not at all take away from the creativity and artistry involved in creating a recipe in the first place, though science can help to some extent there too.)

                                                                                                        While many chefs still go by "feel" in many things, professional cookbooks increasingly point to the scientific study of food to guarantee consistent results.

                                                                                                        I first encountered this in Harold McGee's work, as well as in good bread-baking books, like Jeffrey Hamelman's "Bread," which completely changed my outlook on baking. Yeasted dough is finicky, and if you're a professional baker, you need to bake on a schedule. That requires, for example, always ending up with dough at a particular temperature and hydration level after mixing. Hamelman provides tables and formulas to take into account temperature of ingredients, room temperature, humidity, and even the revolutions-per-minute of your mixer (which adds heat energy to the dough) to end up with dough that is consistently at the temperature you want it.... every time.

                                                                                                        Is this overkill for the home baker? Of course. But if you need to guarantee that you'll get consistently good results every time, as bakeries do, this is the sort of knowledge you need. An old-school baker would be able to approximate this after years of experience, but Hamelman's instructions allow anyone with a few simple tools (like a thermometer) to do it.

                                                                                                        That, to me, is what happens when engineers (or people who think like engineers) cook. And I'm personally very happy they do it, because I feel like I have learned more about why things happen in the kitchen in a few years by understanding the underlying science than I think many cooks learn from a lifetime of trial-and-error.

                                                                                                        1. re: athanasius

                                                                                                          Don't most of us agree that baking is a science and the rest is a craft (not an art)?

                                                                                                          1. re: c oliver

                                                                                                            "Don't most of us agree that baking is a science and the rest is a craft (not an art)?"

                                                                                                            I don't claim to represent "most of us," but here's what I think....

                                                                                                            I'm not sure I understand the distinction you're making here. I also am increasingly suspicious of the claims I often hear about how baking is more scientific, requires chemistry of some sort, etc., but the rest of cooking... not so much.

                                                                                                            Personally, I don't see, for example, how grilling a steak to the perfect doneness *consistently* would require any less emphasis on measurable elements than baking -- consistently marbled meat from a consistent source, consistent type of pan/grill, consistent temperature and timing for cooking, etc. I could say the same thing about making a soup with the "perfect" recipe *consistently* or whatever.

                                                                                                            I think many home cooks think of cooking as something where you can "throw together something" in a pan from what you have in the fridge, but they think baking recipes have to be followed more precisely, or else the "science" will get off... the cake will fall, the bread won't rise, etc.

                                                                                                            I don't agree. This weekend, I made lemon-poppyseed muffins. I've never made them before. I looked online. Almost every recipe had ingredients I didn't have on hand. I wanted to use mostly whole-grain flour. I wanted to use flax. I wanted a somewhat low-fat, low-calorie version, but one that was tasty and moist. I couldn't find a recipe that had even a couple of the characteristics I wanted.

                                                                                                            But I've made muffins before. So I threw together a recipe based on the rough proportions I know to work, and I ended up with decent "healthy" lemon-poppyseed muffins. They're only slightly dry, but I know how to fix that if I choose to do it again. My wife loved them, which is about all that matters.

                                                                                                            I don't see how doing that is any different from using the "craft" of cooking to throw something together. I suppose you usually get to taste stovetop cooking more frequently, but I tasted my batter too, checked its consistency, etc.

                                                                                                            This is a long answer to a short question, but while I'm willing to grant that experience in the "craft" is useful for improvisation or to recover from disaster, I think such skills are equally useful in baking and cooking in general. And I think science is equally useful in baking and cooking in general.

                                                                                                      2. I like the stuff I am reading here. I am considering AllClad Cop.r.chef, coppercore, or the new D5 Allclad Stainless. Does the Coppercore perform better than the copper lined Cop.r.chef. I notice that the copper lining on the Cop.r.chef is very thin and wonder if it performs well or better than the regular Allclad Stainless that I use now. Please write to me directly. Thanks, Mike denvrmike@aol.com

                                                                                                        1 Reply
                                                                                                        1. re: Denver Mike

                                                                                                          Denver Mike: You might also want to look at the de Buyer lines withy copper, including the Prima Matera.

                                                                                                        2. I did a test after noticing on a cooking show (or infomercial?) the cook using one of those cast iron grill pans that spanned two burners. I, like most people (probably), assumed that cast iron would give even heating over the entire surface. After the host started flipping the burgers, as the burgers got further away from the spot directly OVER the burner, they were less-and-less cooked. The host quickly flipped them back to hide this fact.

                                                                                                          I tested my own cast iron and tri-ply cookware with water, flour, omelets and crepes (separately of course). I also used a IR thermometer.

                                                                                                          The tri-ply (either fully clad or disk bottom) heated faster and more evenly than cast iron. The cast iron could HOLD heat longer.

                                                                                                          So while cast iron can make a mean cornbread or stew in the oven, I now know why my pancakes and crepes were uneven on my Lodge cast iron griddle, but fine on a nonstick griddle. (Just make sure the griddle is thick enough to heat evenly).

                                                                                                          (To help cast iron on the stovetop, preheat it in the oven or heat it on high until the edges get close to the temp you want to use and then turn the temp down and let it stabilize).

                                                                                                          1 Reply