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Cast-Iron Seasoning and Carcinogens

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What prevents the oil in the cast-iron seasoning process from becoming carcinogenic -- since temperatures heating the pan typically exceed the smoking points of the high smoking-point oils used for the seasoning process? Is it enough to wipe the excess oil from the pan at the end -- or, when reheated, could the oil 'embedded' into the iron still leach into whatever is being cooked?

(I've diligently sifted through the numerous threads on cast-iron but haven't come up with an answer. It's quite possible of course that no answer's emerged because no one's been so ignorant as to pose the question -- in which case apologies as well as thanks in advance!)

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  1. What temperature would you be planning to use to season this cast iron cookware? Most recommendations I have seen do not call for extremely high heat. The temperatures most often recommended do not exceed 350 degrees, and many sources recommend as low as 220-250 degrees.

    1 Reply
    1. re: angusb

      I always season mine on the stovetop at low heat, but have come across seasoning instructions that call for 500 degrees in the oven -- i.e., over the 400-some-degree smoking point of oils like grapeseed, peanut, rice bran, etc. -- hence this question. Or might such instructions be assuming that the seasoner is using lard?

    2. The simpler version of this question might be: consensus (on many Chowhound cast-iron threads) seems to be that the seasoning process is supposed to smoke -- like crazy, even. But it's also established that when oil smokes it becomes carcinogenic. What am I missing?

      2 Replies
      1. re: sequins

        You may be worrying about this far too much.
        For some reason, people are making a much bigger deal out of seasoning cast iron than they need to.
        No, it doesn't have to smoke.
        No, you don't even need to use any special "process."
        You don't have to do anything beyond cook a bunch of bacon.
        I did that once when I had a new skillet and an oven that didn't work.
        I guess you could also just sauté a lot of veggies if you are a vegetarian - but bacon dripping work waaaayyyyy better than anything to get a skillet in fine shape fast.

        The point of the oil is toslowly fill the pores in the cast iron with oxidized layers of carbon that becomes harder and harder from repeated heating.
        You heat the skillet to the 350 to 400 degree range - about where you'd cook normal food.
        Above that, oil would smoke, break down, and get bitter.
        (That's also where it begins to give off the dreaded free radicals that can potentially increase the risk that might possibly contribute to the chance of your getting cancer if you don't get run over by a bus first.)

        If you heat a skillet above about 500, you won't get a decent layer of seasoning on it.
        In fact, heating it above that might remove any seasoning you have already worked so hard to attain.
        One of the ways to recondition an old skillet that has been ruined, found at auction or a rummage sale, or just gotten gunky, it to put the cast iron through the self-cleaning cycle of an oven.
        Or you can throw it into the embers of a fire.
        The high temperature of the oven or the fireplace will remove all the seasoning and return the cast iron piece to bare metal.
        We did this with all of my family's cast iron after Katrina. It had been submerged in the vile flood waters for weeks. No way of telling what was in that water so we ran everything through the self-cleaning oven and started all over again with the seasoning.
        We ate a lot of BLTs that Autumn.

        1. re: sequins

          First off, let's get real about the carcinogens in oil. The real threat is with consuming foods deep-fried in oil that has been heating all day (like at a fast-food establishment). With that super-size order of fries, you not only get a LOT of fat (which is a both a cancer and heart disease risk-factor) but you get whatever funky carcinogens that have developed.

          The seasoning layer on cast iron is really thin, and for the most part is well bonded to the iron. I just don't see that much getting into your food. My opinion is that the bulk of the health risk comes from the fat that you add to the pan, whatever the pan material.

          A very real carcinogenic threat comes from eating meats that have been smoked, or that have been either grilled or barbecued, particularly if they have charred. Yet I don't see too many folks turning in their grills and smokers.

          Second, there are two schools of thought when it comes to seasoning temps: low and high. If you read the instructions that Lodge provides, you would see that they are recommending oven temps in the 300-350F range. This is not quite hot enough to get the oil to smoke, but it is hot enough to get the oil to polymerize and bond to the iron.

          However, as you have find with a little research, high temps (400-500F) get the process really going. The advantage to the high temp method is that you are less like to get gummy spots where the oil was a little thick. You get a nice hard coating right off the bat. The disadvantage is that the oil is starting to burn at that temperature, and producing lots of smoke (and who knows what else).

          Anything hotter is unproductive, since it burns the oil and the seasoning and leaves you with an unseasoned pan. This is what happes in your oven during the self-clean cycle.

          Personally, I season my stuff on my gas grill and prefer keeping the heat low, but that is just my preference. What little smoke that gets generated stays outside instead of stinking up the house.

        2. Best idea is to just to i follow
          the manufacturer's directions on seasoning.
          It's no more complicated than
          how to boil water. But if it
          worries you,I'd suggest
          using cookware that doesn't require
          seasoning.

          1. The oil isn't carcinogenic, the seasoning is.
            #1: You don't eat the seaoning.
            #2: You'd need to eat a few ounces of seasoning a day for 10 years to double your chances of getting a related cancer.
            #3: There's little to no chemical difference between the seasoning on the pan, and nicely browned foods obtained by broiling, searing, grilling, etc.
            #4: Your body's natural defenses render most small amounts of such materials harmless. The free radicals are counteracted by antioxidants. It's only when you exceed your body's defenses (see ounces a day above) that any carcinogenic effect kicks in.

            In short, it's FUD (Google FUD) spread by cookware companies selling non-cast-iron products.

            If you're that worried about it, don't eat any browned foods. Thanksgiving turkey, toast, grilled steak or hamburgers, grilled fish, etc. Otherwise realize that folks have been eating those things for centuries, and that the seasoning on a pan is made up of the same polymerized and carbonized stuff.

            1. Thanks to all for the well-reasoned assurances. I will stop worrying about it!

              1. I wouldn't be surprised if someone studied the smoke and the seasoning on cast iron pans, and found that it was just as carcinogenic (and/or toxic) as Teflon and aluminum. Lodge probably has a very good ventilation system on their preseasoning oven. But, since most seasoning and use is done at home on a small scale, it is unlikely that anyone will conduct a careful study of this matter. Exposure must vary all over the place - old homes leak like sieves, new ones can be overly airtight, some have vented hoods, others don't. Some use their cast iron daily, others once a month. Some will get similar exposures from backyard grills and smokers. Some use their cast iron to bake cornbread, others to sear steaks (think of all those burnt oil particles in the air).

                I don't worry about, but I think it is a valid question if someone is trying to convince you to throw out all your new-fangled dangerous cookware and replacing it with something more traditional and supposedly safer.

                3 Replies
                1. re: paulj

                  I decided to stop worrying about stuff like this at the end of November, 2007.
                  In Washington, DC, a city of fewer than 600,000, we had 24 pedestrian deaths by the end of November.
                  I have NO idea how many hapless, innocent children and adults walking to work, church, the store or simply strolling along, were run down by buses, taxis, or reckless drivers in December but 24 was plenty in the first eleven months.
                  That had to be more than were killed by Teflon, saccharin, HFCS, Twinkies, red food coloring, Cool Whip, silver dragées, mercury in tuna, and all the other stuff that some bunch of scientists swear will cut me down in my prime.

                  Life is too damned short to worry about every "potential" carcinogen that some Congressional earmark paid some geeks to study.
                  Something that might only raise a chance by 1 in 100,000. Maybe. Perhaps. On a bad day. If my karma is terrible.

                  I could be perfectly healthy and get hit by a bus.

                  1. re: MakingSense

                    You are aptly named, Making Sense!
                    Of course we agree about being "healthy" and getting hit by a bus. There's much too much worry & concern about the "what ifs" that they interfere with life's enjoyment.

                    Want an egg for breakfast? Better not, they're high in cholesterol.
                    Want a drink before dinner? Better not, the alcohol might render you senseless.
                    Want a grilled steak? Better not, the carcinogens may give you cancer.
                    Want a lovely piece of cheese? Better not, cheese is high in fat.
                    Want buttered toast? Better not, saturated fat will give you a heart attack
                    Want a glass of water? Better not, God knows what's in there
                    You can forget desserts unless it is a bunch of grapes; oops, the carbon footprint is a problem..... ad nauseum.

                    We're left to fret about each and every little thing and that stress is much more likely to kill us -- and without the added enjoyment of good food!
                    Basta! If I made New Year's resolutions, mine would be to enjoy each and every mouthful, each and every day,
                    Oh wait, I already do that. I am hale and hearty with great numbers and two thumbs up from my last check-up from a physician who told me to keep doing whatever I'm doing. When I told her that our NYE dinner would be splitting a roasted duck and bottle of champagne she just smiled.

                    I believe that some people really need things to worry about. Food shouldn't be one of them. Food is to enjoy, food is to share with loved ones, food is to savor, food is too precious and important to be left to government GS-1 geeks.

                    L'chayim!

                    1. re: MakingSense

                      Amen.

                  2. Thank you to all who took the time to reply.

                    About 25% of my motivation for posting this question can certainly be chalked up to 'worry', but the other 75% was scientific curiosity. Commonplace statistics about the likeliness of death by bus -- and the well-intentioned but presumptuous cajoling that 'Life is too damned short' to worry -- seem to counter the spirit of inquiry. The question is a legitimate one. If there's insufficient evidence or consensus out there for any answer, simply stating so would be helpful.

                    14 Replies
                    1. re: sequins

                      Although your main purpose may have been "scientific curiosity," your question is one that has been asked over and over again on CH and never seems to be resolved.
                      No amount of reasonable data regarding the improvement of manufacturing techniques, elimination of the use of certain objectionable chemicals, sensible details regarding actual use of Teflon in practice, or other discussion, seems to allay the fears that some people continue to have about the use of non-stick pans.
                      Posters continue to resurrect old materials which bubble to the top of Google searches about prior scare stories concerning Teflon, much of it anecdotal, such as canaries dying.

                      A great deal of the concern is related to the way news is reported. A negative study makes the evening news or the front pages. It is written by a general coverage journalist with little to no scientific background, often from a press release by an interest group which he may or may not credit in the story. That group may have an ax to grind or a message to promote.
                      What is usually lost is the source of the study, how reputable the source was, how extensive it was and how valid the results might be.
                      What is virtually never reported is who paid for the study.
                      If a study includes only 20 people and 5 of them show a certain result, that is a 25% increase, which seems very large - if the synopsis say "a 25% increase was reported." But we are told NOTHING more about the methodology of the study.
                      If the study is later discredited, there are NO stories or they do not register in the public consciousness. They already KNOW that this stuff is going to KILL them.
                      Corrections and retractions virtually NEVER make it to the top of Google searches because nobody is as interested in them as they are in the bad news.

                      An example are reports of links between aluminum and various diseases. http://www.snopes.com/movies/actors/v...
                      There has been a recent one about aluminum cookware and Alzheimer's. There was later shown to be no link at all. The scientist who reported it had based his assumption on aluminum levels in autopsies. However, aluminum is the most common element on earth and there are concentrations of it in everyone whether they have used aluminum pans or not. Many people still refuse to use aluminum pans or foil wrapping and can not be persuaded otherwise. http://www.sciam.com/article.cfm?id=i...
                      These same types of stories persist for plastics and many other products.

                      When a product presents a REAL and SERIOUS health hazard, it is taken off the market.
                      Until then, your canary shouldn't be in the kitchen and pans shouldn't be heated over 500 degrees because you'll burn the food.
                      Everything is going to catch on fire and the smoke will kill the canary.

                      1. re: MakingSense

                        MakingSense, I am a skeptic and a scientist myself, and the son of a veterinarian, but "canaries dying" is much more than a scare story. It is a well-documented danger of nonstick pans. The fact that there are a lot of people publishing the stories of their birds dying (the anecdotal evidence you dismiss) is not surprising--they are upset. I couldn't find a warning from DuPont doing a quick search, but here is one from T-fal: http://www.t-falusa.com/Tefal+magazin... They repeat the advice of veterinarians, which is to keep your birds away from the kitchen and to make sure your pans don't overheat. The fact that T-fal and others are now throwing into the mix the fact that birds are "sensitive to" normal kitchen fumes does not negate the fact that even slightly overheated nonstick pans kill birds.

                        1. re: angusb

                          I thought this discussion was about cast iron seasoning, not non-stick pans.

                          1. re: angusb

                            Yes, "upset" people may publish stories about dead birds. That does not necessarily make them "well-documented." They remain anecdotal because there may well have been other UNREPORTED factors involved.
                            Any vet would caution a bird owner that a kitchen isn't the best place to keep a sensitive pet bird.
                            Most of us have filled a kitchen with smoke when we've done something pretty simple like searing a steak or breaking our concentration while cooking.

                            It's probable that in a controlled environment, Telfon or any number of chemicals can be heated to a temperature that would kill kittens, birds, toddlers, or adults.
                            In normal use and at normal cooking temperatures, most cooking oils smoke at less than 500 degrees and combust at slightly above that temperature causing grease fires and/or burning the food that is being cooked. Substantial amounts of smoke are created.
                            This would happen as easily with "slightly overheated" standard pans as with non-stick ones.

                            It is reasonable to assume that the dangers of Teflon coatings may have been overstated by the anecdotal reports.
                            Better conclusions may be that one should not overheat any pan nor keep a bird in the kitchen.

                            1. re: MakingSense

                              Oh, MakingSense, I intend to be Czarina of the Universe in the not-too-distant future. What cabinet position do you want? I think Secretary of Health would too limit your oh-so-wise-ness. How about Dictator of Making Sense. We are going to have absolute power BTW. Interested?

                            2. re: angusb

                              I just read the article from your link , it says a pan won't go over 575 degrees on a normal stove? I've never tried but I think if I left a pan on a 19,000 btu burner for an hour it might just go over 575. Now I have to bring my non-contact thermometer from work and see how hot the pans get VS time on the burner

                              1. re: Dave5440

                                Save yourself the trouble, there are a couple of posts where people left dry enameled cast iron pieces on an electric coil stove top and melted the enamel, that's waaaaay over 575 at least as long as we're talking °F. When this was reported I did a web search to see how hot a resistance coil can get, and yes they can get hot enough to melt the enamel. I have to admit I was shocked, I really thought that would be impossible, but it is.

                              2. re: angusb

                                One phrase I'd change:
                                Not "When a product presents a REAL and SERIOUS health hazard, it is taken off the market."
                                SOME TIME AFTER a product presents a real and serious health hazard, it is OFTEN taken off the market.

                                (I also disagree with the sweeping generalization about the quality of news coverage of studies, although I often agree with MakingSense on other issues.)

                              3. re: MakingSense

                                err... for starters on scientific lecturing.. you might want to get certain facts straight -- i.e. Aluminum is not the most abundant element on earth, at least by most measurement methods I am familiar with.

                                1. re: mateo21

                                  How about refining the statement to : most abundant metal? Oxygen and silicon are more abundant, but not metals.

                                  1. re: paulj

                                    paulj: "How about refining [rimshot, please] the statement to : most abundant metal?"

                                    Gosh I love Zombie threads. While I leave it to others to raise the undead, I'll happily march along...

                                    AL may be the third most common element and most common metall-IC element, but didn't freely exist as a metal until fewer than 200 years ago, when folks started figuring out how to refine it.

                                    This thread originated on the safety of CI seasoning, but the AL detour is extremely illustrative of the fact that NO ONE REALLY KNOWS the safety of a simple metal that has been widely used now for over 100 years. See, the Health Concerns section (and cited articles) of http://en.wikipedia.org/wiki/Aluminium However, that paucity doesn't seem to restrain folks from claiming to know, and spreading nonsense like: "If it were dangerous, it wouldn't be on the market." I'm not saying you have, but we should all be a little more circumspect when it comes to jumping people's s@#$ about safety concerns, when the true knowledge is either tissue-thin or suppressed. There are too many counterexamples to be funny: direct cig smoke, lead canning solder, CFCs, secondhand smoke, etc., etc. There may be others on their way; see, e.g., http://www.cancer.gov/cancertopics/fa...

                                    So, back on thread, I'm going to avoid breathing the smoke thrown off by heated oils/fats in the CI seasoning process.

                                    1. re: kaleokahu

                                      The reason why I think the abundance argument is relevant is that it means we must breath and ingest a fair amount of aluminum via dust and dirt, maybe even compounds in root vegetables. Your point about the newness of metalic aluminum is well taken, but how much elemental aluminum do we ingest via cookware? Bare aluminum is rarely bare; it quickly develops a strongly adhering aluminum oxide layer. Does that aluminum oxide behave any different from other compounds that contain aluminum?

                                      1. re: paulj

                                        paulj: It's above my pay grade to even guess about intake/metabolism/storage of AL and its oxides in the body from the peck of dirt we all eat/breathe. I know that most natural aluminum in the earth is chemically bound up into hundreds of other compounds besides bauxite, that a ton of bauxite will only yield about 500 pounds of aluminum; and that it takes prodigious amounts of energy to smelt away the impurities. And you're left with a lot of toxic red mud when you're done.

                                        This turn in the discussion is appropos of a subset of the endless PTFE debates. That is, it is worth pondering how little PFOA and other degradation products enters our bodies from PTFE cookware [mis]use, and concluding that number pales in comparison to the PFOA, etc. we may be getting from the industrial manufacturing process and their wastes. In the final analysis, does it make any difference that the finished cookware ITSELF is safe[r], when its manufacture is really [more] to blame?

                                2. re: MakingSense

                                  "When a product presents a REAL and SERIOUS health hazard, it is taken off the market"

                                  Umm--like tobacco?

                              4. When oil smokes it produces minute amounts of carcinogens, if you choose to season at a higher temp (my preference), just make sure you have plenty of ventilation and you'll be fine.

                                1. Great question. Here's the answer! Never saw this anywhere else:

                                  http://sherylcanter.com/wordpress/201...

                                  3 Replies
                                  1. re: permutations

                                    Again I say, hooey!

                                    1. re: permutations

                                      From the article:
                                      " The free radicals then “crosslink” to form the tough, hard film you see in a well-seasoned pan"
                                      WRONG! It's the hydrocarbon chains that link up after releasing the free radical, not the free rads themselves. The free rads are generally hydroxyl (one oxygen and hydrogen) which tend to pull another hydrogen atom off the hydrocarbon chains, making them more carbon-dense, thus closer to the pyrolytic carbon that eventually becomes your seasoning.

                                      1. re: ThreeGigs

                                        You're going to make my head explode.
                                        The answer is that whatever there is in bacon "eventually becomes your seasoning."

                                    2. There IS no "excess oil" to wipe from cast iron properly seasoned, at the end. Start with a very light coating (wipe, and wipe again, before you even put it in the oven; for truly beautiful finishes--with no spotting or lines--wipe several times during the process, as well) and once it's carbonized, there will be nothing left on the pan/skillet but the hard, baked on finish, itself.

                                      I've been following the suggestions put forth by passionate cast iron collectors (members of the Wagner and Griswold society) with great results, for over a year, now. I've probably completely stripped and re-seasoned 50 pieces of cast iron, this year: First, I remove the old finish (on thrift store and auction finds) via various methods (self-cleaning oven cycle, lye dip, EasyOff treatment, etc.). I wash in soap (the only time I use soap) and then place the clean, dry, untreated item in a pre-heated oven (to avoid rusting; gas ovens often start out damp) for an hour at about 450. Remove, and let cool down...Then, I coat lightly but completely with either olive oil, or Crisco, wipe wipe wipe, and place the item back in the oven and turn the heat up to about 475--500 degrees. You DO get a lot of smoke for a few minutes. This is absolutely necessary for the carbonization process, which ensures a good, hard, shiny, DRY season. But it's soon gone (open your windows) and I let the item bake for another hour, total, then cool down in the oven.

                                      What I get from this process is beautiful: black as onyx, shiny, slick and yet NOT GREASY! Then, I exercise care for the first few times I used the cast iron (avoiding acid items or much liquid), coat the interior of the piece lightly with PAM (wiped off; any oil will work but PAM is easy and less prone to turn rancid if you don't use the item for a long time) and, voila! You have a gloriously seasoned piece of cast iron that just gets better and better with use.

                                      Here's an example: both these old griswold pans were cruddy and rusty, when I bought them. What you see in the pic are pans that are gleaming and black, NOT sticky or oily, and very smooth. (this is my photobucket account):

                                      http://i33.photobucket.com/albums/d57...

                                      1. Burned oil is not seasoning. I've recommended in another thread a protocol of sanding the interior of a new cast iron article of cookware from 100 grit through at least 220 grit sandpaper. The most rigorous seasoning routine in the world is a waste of time on modern, roughly cast cast-iron.

                                        Sand it smooth. Really smooth. THEN follow a reasonable seasoning protocol.

                                        1 Reply
                                        1. re: CharlieTheCook

                                          http://www.youtube.com/watch?v=GrZMOg...
                                          Here's a video showing a new pan performing reasonably well.

                                        2. This reminds me of a study done in the 1960s. They strapped nickels, pennies, and quarters to the backs of mice.....guess what? The mice developed cancers. The study was presented as "money causes cancer."