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Confused about thermal shock and cast iron?

e
Eivuwan Oct 7, 2009 10:13 PM

Hi all, I am planning to buy some preseasoned lodge cast iron skillets and have been researching a lot about cast iron use and care. I have a what I believe to be a cast iron wok already so I am comfortable with cast iron. I understand that you're not suppose to put cold water on a hot cast iron skillet or it'll crack (although the water didn't bother my wok), but what about heating up a skillet with high heat on a gas stove? Is that ok or should I start with low heat/medium heat first and then crank it up to high heat? Any help would be appreciated.

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  1. Robin Joy Oct 8, 2009 12:16 AM

    Broadly speaking, the rate of heat transfer from hot gas (e.g. flame) to cold iron is less than the rate of transfer from hot iron to cold liquid. The main danger lies in putting a hot pan into a basin, or even a puddle, of cold water. The layer of iron in direct contact with the cold water will cool rapidly, and contract more quickly than the inner core of the iron, leading to stress and possibly failure. Same goes for glass, especially thick glass. Manufacturing inconsistencies or faults make all this worse.

    That said, I think that the slow heat-up might be wise if you are worried.

    1 Reply
    1. re: Robin Joy
      Soop Oct 8, 2009 03:29 AM

      See, that's quite similar to what I was thinking when deglazing. But a puddle of cold water will be heated by the pan far more quickly than the heavy pan would be cooled by the water.
      I can't see that it would be a problem with CI, but don't put it in the sink until it's cool.

      Eivuwan; Cast iron warms slowly but retains the heat. I don't use mine on very high heat, more about 3/4 of the dial. It still heats up really hot, hotter than anything else (I use the hand-over-the-pan method) that I've cooked with.

      Also, it retains its heat well enough to cook eggs after being taken off the gas, no problem.

    2. monku Oct 8, 2009 05:13 AM

      Now I'm confused...
      Having used cast iron for 40+ years and reading CH posts about cast iron thermal shock and high heat it's a revelation to me.
      I've never had a failure of a cast iron pan or pot and I've been taking them from high heat and dropping them into a dish pan of water or putting water into them when finished cooking to help clean them (makes a neat sound). Having inherited some cast iron stuff and having bought a few pieces I've never remembered a warning label on the directions or no one ever told me what you shouldn't do.

      9 Replies
      1. re: monku
        Soop Oct 8, 2009 05:30 AM

        I can imagine it's quite satisfying... Mine is enamelled so I wouldn't dare.

        And now you say it, they used to slake molten iron the same way in sword making. IDK.

        1. re: Soop
          monku Oct 8, 2009 05:39 AM

          Isn't that how they temper steel and other metals?

          1. re: monku
            Robin Joy Oct 8, 2009 05:53 AM

            If I remember school correctly then controlled tempering of iron is achieved by using oil of some sort at various temperatures. Crude use of plain water......Oh. Off subject a bit!

            1. re: Robin Joy
              monku Oct 8, 2009 05:58 AM

              Yes, after I posted I remembered something about tempering with oil.
              But, back in the days maybe water was used before there was oil? But, whatever I saw on TV about tempering it looked like they took a red hot piece of steel and whatever they put it into it made some big sizzling sound like I get when I put my hot cast iron pan into the dish pan of water.

              1. re: monku
                Soop Oct 8, 2009 06:48 AM

                Can you check if your pan is flat? Don't know if it would make that much difference at that temp.

                1. re: Soop
                  monku Oct 8, 2009 04:46 PM

                  According to the tips on the Lodge Cast Iron website it says you should pre-heat the pan slowly and avoid thermal shock which will cause cracking or warping.
                  http://www.lodgemfg.com/use-care-seas...

                  I never saw those directions and as badly as I seem to be abusing my cast iron stuff, I've never had a problem.

                  Why change when it's worked for 40+ years. Flat as a board and I'd challenge anyone who can destroy a cast iron pot or pan.
                  Heck, I've used cast iron frying pans to hammer tent pegs into the ground.

                  1. re: monku
                    p
                    pass Oct 8, 2009 05:05 PM

                    It's not a myth, I've come across CI pans that don't sit flat. If its enamelled then you'll really ruin it. Everyone advises against it for a reason.

            2. re: monku
              Paulustrious Oct 8, 2009 03:30 PM

              You temper in different materials and at different temperatures to create different effects, depending on whether you want toughness, hardness, ductility, stress relief, corrosion resistance, resistance to fatigue and so on. etc. You can also preheat oil to temper at a higher temperature. In the aircraft industry we used to temper some stuff in liquid cyanide salts, but I cannot for the life of me remember what that did.

              1. re: Paulustrious
                k
                Kelli2006 Oct 10, 2009 03:41 PM

                Cyanide carbarizing is used to surface harden the part by drawing the very hard carbon particles to the surface. It gives the part abrasion resistance while protecting the ductility of the parts interior.

                IMVHO< it's more important to cool the part before submerging it in cold water because the thermal conductivity of water is far greater.

        2. Chemicalkinetics Oct 8, 2009 11:03 AM

          Lodge cast iron skillets are pretty good, I think. Although I only have their two dutch ovens. I preseason my two dutch ovens because sometime they don't do such a good job. I wish they would just sell unseasoned cast iron, so I don't have to work twice (burn off the original seasoning surface and then reapply my own).

          Cast iron woks are different sometime. If you are talking about Lodge cast iron wok, then they are not that different from other Lodge cast iron cookware. However, if you have a traditional cast iron wok, then it is thinner. Traditional cast iron woks are made thinner, so that you can skill more it with one hand when you cook.

          1. MikeB3542 Oct 9, 2009 07:28 PM

            Cast iron may be a metal, but it's mechanical properties are more like ceramic:strong in compression, weak and brittle in tension. Because it lacks the crystalline structure of steel or aluminum, heat treatments like quenching in water, oils, or solutions of cyanide (nitriding) don't do much to help cast iron.

            If you have been dunking hot cast iron pans in a sinkful of col water for years, and haven't broken or massively warped one yet, I would chalk it up to dumb luck.

            2 Replies
            1. re: MikeB3542
              Paulustrious Oct 10, 2009 03:56 AM

              Odd though that we have not had anyone say they doused a cast iron skillet and it shattered. I've always used a 'sprinkle' method on my hot CI pans and griddles. Much easier to clean when they are really hot. And I am sure it is to the horror of other CHers, I use steel wool. to clean. It doesn't take the seasoning off my pans. Or at least it is being replaced at the rate it is being abraded.

              1. re: Paulustrious
                b
                bchick Jan 2, 2010 07:17 PM

                I've never seen one "shattered" by being put in cold water, but I think a friend of mine knows someone who did it, and we do have one in our house that is cracked because someone put it in the sink while it was still very hot and ran cold water into it.

                From what I understand, cast iron is like ceramic or glass, it can go *poof* if you do certain things to it, but won't always. The warning to not putting into cold water is because it *can* (but won't always) cause it to crack or shatter. Kinda like the warnings that you sometimes hear about super-heating water in the microwave. I spent years using the micro to boil water for instant rice and such with no problem, and then one day I took water out of the microwave that didn't appear to have even reach boiling, dumped in the rice and had a volcano of water and instant flavored rice. Burned my hand (the one pouring the rice) pretty good and made a huge mess in my dorm room.

                Better safe than sorry. There is no good reason to put a hot pan in contact with much colder water. Plenty of methods for cleaning that won't shock the metal.

            2. Zeldog Oct 9, 2009 08:07 PM

              This sounds like a good test for Mythbusters. They could heat a cast iron skillet to red hot with welding torches and pour liquid nitrogen on them to make them shatter. I use cast iron for all high temperature cooking and my preferred method to clean them is to put them under a stream of cold water as soon as I remove the food (this removes most of the grease and shocks loose a lot of crud without any scouring but leaves the seasoning intact). This works especially well when searing at very high temperatures.

              I've been using this method for decades on at least 3 different pans, including a rather thin one (no brand marking, made in Taiwan), and they all are intact and sit flat to this day. Theoretically, you might be able break any piece of cast iron if you heat it high enough and cool it fast and unevenly, but I don't think this is something to worry about with cast iron cookware. The pans are just too thick and the cooking temperatures not that high and room temperature water is not that cold. Relax, Eivuwan.

              But the reason you shouldn't be deglazing cast iron pans is they just don't make good fonde. The crusty bits mix with the seasoning and you end up with a nasty looking grey sauce. Stainless is best for that particular task. I have exactly one stainless skillet and the only time I use it is when I need to deglaze.

              1. PBSF Oct 9, 2009 08:42 PM

                Guess I am another one of those "dumb" luck when it comes to cast iron. I've been using my 3 skillets for over 30 years, heating them over high heat, putting them in cold water while still red hot after uses and they are still in one piece and perfectly flat. I also managed a restaurant kitchen where we used case iron skillets to cook a few specific things and the through the abuses they took from cooks and dishwashers, none has ever cracked or warped.

                2 Replies
                1. re: PBSF
                  Zeldog Oct 9, 2009 08:56 PM

                  Yup. In my experience, the only practical way to crack a piece of cast iron is to hit it really hard with a large hammer (yes, I did this to a found skillet that I considered restoring but had too much surface corrosion).

                  1. re: Zeldog
                    Ambimom Oct 10, 2009 06:17 AM

                    I'm with you zeldog! I think there is so much "advice" about cast iron that is just plain ridiculous. If it were all that precious to use and maintain, so much of it wouldn't be around today to become the darling of the vintage Griswold, Wagner groupies. I deglaze my cast iron with water regularly; cook tomatoes in my naked cast iron, season with olive oil, etc. etc. etc. My pans are just fine, thank you. Mine are not being collected, they are being used.

                2. Chemicalkinetics Oct 10, 2009 07:17 AM

                  Look, I think people get confused being about "can crack" vs "will crack". Cast iron cookware, when experiencing thermal shock, CAN crack but there is very rare and usually happens after multiple mistreatments. I don't know a single person (in person) which has cast iron cracks on him/her. Again, it is very difficult to crack cast iron. It is possible, but very rare even if misuse. On the other hand, it is essential impossible to crack a stainless steel or aluminum cookware. They can warp.

                  There is a reason a basic difference between cracking and warping. When an aluminum cookware warps, there is no serious dangerous. When a cast iron cookware cracks, you can have very hot foods spilling everywhere and cause some real hazards.

                  4 Replies
                  1. re: Chemicalkinetics
                    k
                    Kelli2006 Oct 10, 2009 03:45 PM

                    Cast iron, either grey or ductile, is far more brittle than steel or aluminum alloys, and this is because of the higher amounts of carbon that they contain.

                    Yes, I'm a geek.

                    1. re: Kelli2006
                      Chemicalkinetics Oct 10, 2009 06:24 PM

                      Hi Kelli,

                      I know I know, which is why I said steel and aluminum are essentially cannot be cracked in a kitchen. However, even cast iron is brittle, cast iron cookware do not scatter left and right. It can happen, but not as often as people think. The problem is that when it does happen, it can cause harms.

                    2. re: Chemicalkinetics
                      b
                      Beckyleach Oct 10, 2009 11:13 PM

                      I've been collecting vintage cast iron for a while, now, and I CAN attest to the fact that is fragile--at least the older, thinner, higher quality pieces. I've had cast iron muffin pans arrive--after the USPO has finished with them--cracked to smithereens. I've accidentally cracked the bottom out of an 1860's skillet by subjecting it to thermal shock. I've seen plenty of larger ERIE pans (pre-Griswold, with very thin walls) with hairline cracks near the handles...

                      That said, I still deglaze my good stuff (AFTER it's well-seasoned) and I do cook chili in my 100 year old dutch oven (even with tomatoes; Midwestern-style ;-). I do not take the chance on cold water to clean, however. Why not just set it in the sink and then run HOT water in it, instead? Is it somehow more difficult to turn on the hot tap, than the cold?

                      1. re: Beckyleach
                        tanuki soup Oct 11, 2009 04:46 AM

                        "Why not just set it in the sink and then run HOT water in it, instead? Is it somehow more difficult to turn on the hot tap, than the cold?"

                        Common sense prevails. Why abuse your cookware when it's so easy to treat it nice?

                        After I've removed the food from my cast iron skillets, I turn off the heat, fill up a large measuring cup with HOT water, pour it into the skillet sitting on the cooktop, and go enjoy my dinner. Cleanup is a snap, and I haven't damaged either my skillets or their seasoning.

                    3. e
                      Eivuwan Oct 12, 2009 07:48 AM

                      Thank you for all the responses guys. I think I'll just treat my cast iron with care but not be too paranoid about it. Anyway, all this talk about thermal shock makes me wonder about what happens when cooking. For those of you who would not put cold water in cast iron after cooking, what about during cooking? Wouldn't putting room temperature water in a hot skillet cause thermal shock? I just don't understand why people would use cast iron at all if it's that fussy of a cookware (can't put acidic foods in it, have to be aware of thermal shock, etc). Like I said, I've used a cast iron wok, and never realize all these problems with cast iron until I started doing some research on cast iron skillets.

                      2 Replies
                      1. re: Eivuwan
                        Soop Oct 12, 2009 07:57 AM

                        Check this thread about deglazing: http://chowhound.chow.com/topics/654876
                        We don't really reach any firm conclusions, but it's interesting.

                        1. re: Eivuwan
                          MikeB3542 Oct 12, 2009 07:58 AM

                          Cast iron really isn't that fussy -- but it rewards TLC.

                          Thermal shock is an issue with all cookware -- metals warp and ceramics break.

                          Most foods aren't so acidic that they can't be cooked in seasoned cast iron -- long simmering tomatoes, wine or citrus can cause some funky tastes if the seasoning wears out, otherwise, it ought not be babied.

                        2. greygarious Oct 12, 2009 10:13 PM

                          Recently, QVC recalled their Paula Deen line of cast iron cookware because it was cracking and shattering but I know NONE of the details.

                          2 Replies
                          1. re: greygarious
                            Zeldog Oct 14, 2009 05:58 PM

                            I'm shocked! Shocked to hear that QVC sells cheap crap. But I hope Paula Deen enjoys the payoff she got for letting them use her name.

                            1. re: greygarious
                              Paulustrious Oct 15, 2009 09:15 AM

                              The one advantage is that it was all mail order so they can contact all the purchasers. To be fair, it looks like they were proactive in terms of the recall.

                            2. p
                              pletty Oct 15, 2009 08:26 PM

                              I've never cracked a good old cast iron skillet and I've abused them. I turn the propane up high right away under my cast iron skillets and never had a problem. Think about it, people started using cast iron long before there were controls on their heating sources! And what about cooking up a stew over a camp fire in a cast iron dutch oven? A word of warning on enameled cast iron however--my husband dropped a 5 quart enameled cast iron Le Creuset dutch oven-- it dented my wood floor and--it cracked! Enameled cast iron is more sensitive to temperature changes than unenameled, so if you use that you should start with a low flame. I've been wondering if I did something to weaken the Le Creuset that caused it to crack.

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