I am seasoning a carbon steel wok and from what I understand it basically involves heating cooking oil on it until it gets to the smoke point and then forms a polymerized layer that makes it like a non stick pan. I have also heard that as oil gets heated close to and past the smoke point it breaks down releasing free radicals and other unhealthy compounds. My question is that when the heated oil polymerizes do these compounds get permanently locked up in the polymer or will they eventually get into the food cooked in the pan?
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4 Answers
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I read several articles in the topic in the past 5 hours, and I have a different conclusion than the other answerer.
My experience that the TG polymer layer on the surface of your wok is far from being stable. Every time you use it, smaller or bigger particles of the polymer can end up in your food. Some of them are even visible, that's why I stopped using a wok a long time ago. If you want to use a seasoned wok no matter what, then do the seasoning with an oil high in polyunsaturated fatty acids (e.g. flax seed oil), so the polymer will be somewhat more stable, because of the additional bonds, but there is no guarantee that it won't break down in time. Don't use these heat sensitive oils for cooking, they are good only for seasoning or for cold salads.
High polymers can be absorbed depending on whether the enzymes of the digestive tract can handle them. For example starch is a high polymer of glucose and amylases can easily hydrolize it, while cellulose is a different high polymer of glucose, which we don't have the enzymes to digest. As of TG polymers, they contain mostly fatty acid monomers, dimers and trimers. So the polimerization is far from being complete, you won't get long fatty acid polymers by cutting down the glycerols with a lipase. According to the articles I read, lipases can hydrolize around 10-50% of the polymers (they are inhibited by them at some degree), so the resulting dimers, trimers, oxidized monomers, cyclic monomers, etc. created in the seasoning process, can be absorbed. It is hard to find studies about their health effect, but they are not considered healthy.
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1$\begingroup$ Any cook can tell you, that seasoning a pan is not a permanent, but ongoing affair. High heat, acidic food and mechanical damage can and does occur, which is why you need to season your pan on a regular basis. So it is clear, that some of this stuff ends up in your food, no way around that. $\endgroup$ Commented Aug 14, 2019 at 18:03
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If you use fresh cooking oil containing unsaturated fats (like olive or canola oil) to season your pan, it will thermally polymerize to form a stable layer that gives the cooking surface its nonstick properties. Note that a saturated fat like coconut oil, lard, or ghee will not work very well or at all for this, since it does not have any double bonds to undergo polymerization. The radical formation you are concerned about results over time from air oxidation of unsaturated fats to form peroxides--these in turn break down to give aldehydes and acids that cause the bad flavor of rancid fat, and have adverse health effects. (Not a problem for coconut oil.) Heating fresh oil in a pan to create a nonstick coating may result in some air oxidation in addition to polymer formation, but I think it is not a big cause for concern. High polymers are generally nontoxic because the body does not absorb them.
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1$\begingroup$ I am not sure I understand your answer. I am pretty sure, that heating oil above its smoke point is pretty bad for your health and as far as I know this is exactly what produces trans fats, please correct me if I am wrong. $\endgroup$ Commented Aug 14, 2019 at 17:59
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1$\begingroup$ @user1721135 No this is not how trans fats are created. And, since the point of seasoning a pan is to create a semi-permanent coating not to cook food, the concerns are irrelevant if the treated pan is washed before you cook with it. $\endgroup$ Commented Mar 30, 2023 at 10:01
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Based on inf3rno's answer, this is from "Deep Frying Chemistry, Nutrition, and Practical Applications" by Michael Erickson
Digestibility of oxidized fatty acid monomers was considerably high, averaging 76.6%. Among polymeric fatty acids, nonpolar dimers had the lowest digestibility (10.9% on average),whereas oxidized dimers and polymers possessed higher apparent absorbability than expected, ranging from 22.7-49.6% (96).
Basically, the question around all safe cookware questions is, "is a coating of X on the surface" considered safe. In stainless steel it would be chromium oxide. Nonstick coatings are manmade thermoplastic polymers. Glass is silicon dioxide. There seems to be a blind consideration of "cast iron" as safe yet it is quite difficult to figure out what the coating actually is, so this question of asking if it releases free radicals makes a lot of sense.
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3$\begingroup$ While this is interesting, I don't see how it actually answers the question. $\endgroup$– Martin - マーチン ♦Commented Mar 26, 2023 at 23:02
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$\begingroup$ I don't have enough points to comment on the above post. $\endgroup$– wkwCommented Mar 29, 2023 at 21:23
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1$\begingroup$ My train of thought was not explained well. Since inf3rno stated that "dimers, trimers, oxidized monomers, cyclic monomers" are created, I wanted to quantify how well they are absorbed. I agree that they are not healthy. $\endgroup$– wkwCommented Mar 29, 2023 at 21:24
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Seasoning a pan correctly with a high smoke point, majority unsaturated, oil will result in a pretty stable polymer bound to the pan well, unless disturbed by an acid like lemon or tomato juice.
Polymerisation generally occurs in most of the oils commonly used below their smoke point, and at or above the smoke point you will mainly get carbonisation of the oil. In old fashioned seasoning methods a mixture of polymerisation and carbonisation occurs to create layers of material that are similar in performance to non-stick pans. Seasoning should however, be done with an oil like avocado oil at a temperature below its smoke point of >420°F and above its polymerisation point of around 350°F to avoid carbonisation and get the most stable layer of protection for the pan.
Flax oil is a terrible choice for seasoning as the seasoning layer is very brittle and therefore can flake off into food easily (possibly due to a combination of its high polyunsaturated fat content and low smoke point). As stated, saturated fats are also inadequate for polymerisation.
The potential harmfulness of the seasoning is a difficult question to answer as I imagine the variation of seasoning oil, technique, quality and pan usage greatly affect the type and release of compounds, created in the seasoning process, into food and therefore your adsorption and exposure to them. However any risk must be weighed against not only alternative cookware but also the exposure to chemicals created in the heating of oil during the cooking process - such as ketones, aldehydes, polycyclic aromatic hydrocarbons (PAHs), hydroperoxides and epoxides.
