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Oct 3, 2010 05:20 PM

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?

        39 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.

                                1. re: mrnelso

                                  Has anybody had any luck with the heat diffusers on the market? I bought a 1/8" thick 9" x 9 " copper plate which seems to even out the heat under my cast iron pan beautifully.

                              2. 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.