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A very common claim is that once you start cooking with a cast-iron pan, you never really need to season it again. As you cook, the seasoning just builds up. However, the way I understand it, seasoning only happens when you heat the oil so much that it starts to smoke. However, smoking oil has many carcinogens, and you're not supposed to eat it. So how does the seasoning build up if you never heat the pan enough (while cooking) for the seasoning process?

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  • Welcome to SA, Blue! However, topics about healtcare, such as carcinogens, are strictly off-topic for SA. Can you edit your question to remove that part? Thanks. – FuzzyChef Oct 5 '20 at 23:13
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    @FuzzyChef Hmm but I don't see how to do that without changing the core of the question. My question is not really about healthcare though; I think it's not a question that oil heated above its smoke point is toxic, and it's a common advice in cooking to avoid it. I'm just asking about this advice in relation to the other advice of "don't worry about seasoning, the pan will get seasoned as you cook." – Blue Oct 6 '20 at 15:28
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Yes, the two pieces of advice are contradictory. You have to choose which one you prefer to follow. If you decide to only use your pan below the smoke temperature of oil, the seasoning will not build up during cooking.

In typical use, people do heat their pans above the smoking point, and the seasoning does build up. This is how cooking has been done for centuries, with tasty results, while cooking without heating the oil up produces not-very-exciting results for certain foods. People can choose to use low-heat cooking methods and avoid the "smoke point" part too, but that is not what usually happens. There are many factors why more people use the "high heat that seasons" approach:

  • They have never heard the "smoking point" advice and use their cast iron pans the usual way
  • They are not aware that they are heating it above the smoke point
  • They know the "smoking point" advice and choose to disregard it and cook the usual way
  • They would like to follow the "smoking point" advice but it is physically very difficult to do it with a cast iron pan
  • (Kinda combination of the last two) They are aware of the difficulties of remaining below the smoking point in a cast iron pan, and choose to use a different pan when they want to stay below the smoking point.

Because of the last one, I would suggest that, if you prefer to follow the "smoking point" advice, you switch to a different type of cookware.

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  • Thanks for your clear answer. I prefer the smoking point advice, but I think I'll continue using cast iron. I cook eggs and fries in it on (mostly low) hear, and they come out better than in other pans. I've heard cast iron can also be good for baking, but I've yet to try it. – Blue Oct 6 '20 at 15:30
  • Hmm interesting, I would expect that eggs would stick if you keep the temperature below the smoking point. Have you checked the actual temperature, or do you simply assume you are staying below? – rumtscho Oct 6 '20 at 15:41
  • The eggs do stick somewhat... when making scrambled eggs for 3 people I sometimes add an extra small egg to account for what sticks. But the taste is really good. But do you cook eggs on a temperature high enough to smoke oil? I don't measure the temperature, but usually I keep it on low for a while until the inside is cooked, and then I may put it on medium for a minute to crisp the outside a little. – Blue Oct 6 '20 at 15:46
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I heat my cast iron pans to the smoking point while cooking in them. Indeed, being able to heat them to 250C/450F (or higher) is a big part of the reason to own a cast iron pan in the first place.

However, you don't generally build up your layers of seasoning while cooking in the pan. Instead, where you build it up is through the brief reseasoning you do after every cleaning, by heating and oiling the pan until it smokes.

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Rather than doing a large dedicated seasoning "top-up" or trying to season while cooking (by reaching the smoke point), I opt to cook as I normally would and then perform a quick seasoning after washing my pan.

Usual steps I take when cooking with my cast iron (inspired by Kenji Lopez Alt. ):

  1. Cook food (e.g. scrambled eggs on a very low temp)
  2. Wash with hot soapy water
  3. Wipe mostly dry with towel and place pan back on medium high heat
  4. Wipe pan all over with dedicated oily rag and then use "clean" side to wipe most of the oil off (like you accidentally put the oil on and are trying to remove it)
  5. Let pan reach smoking point and remove from heat
  6. One final light wipe with the oily rag to protect the pan in between uses
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  • Thanks for the sound advice. I considered this idea, but I think one detriment is that you will have a smell and unhealthy smoke throughout the house every time you do this. Also, the next time you use the cast iron, do you rinse or wipe it so that you remove oil which may not have polymerized from last time? – Blue Oct 7 '20 at 13:45
  • When you bring it to smoking on the stove as a one off, it should only just start lightly smoking. Depending on your burner it may only take 5 min or so. Thats the other benefit of this method, no leaving the pan in a hot oven for hours and filling the house with smoke :) nope, the amount of non-polymerised oil left on the pan is negligible (should be hardly noticable) so I never bother. With that said, if I'd left the pan in the cupboard for months and it had gone sticky, then I may give it either a quick wash or heat cycle, but I'm yet to leave my pan unused for more than a few days – ljden Oct 7 '20 at 20:50
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Several strands to this question...

  • Carcinogens: I'm not a specialist but basically burnt carbon (charcoal) and free radicals (broken down oil) should be avoided in large quantities. You'll get both if you overheat oil in cast iron and then burn the protein you're cooking. Is it dangerous? I would read up more but it's not of my everyday worries...

  • Seasoning: when I got my first set of cast iron cookware I obsessed about seasoning, burning lots of oil in the process and spending hours trying to get to 'blackness'. It was all a bit of a waste of time: keep cooking in the same pan at normal (high) temperature and minimise washing. If you can wipe clean with a paper towel, that's your preferred approach. If it has some burnt elements, then soak in warm water without soap and scrub with scotch brite or an equivalent scourer. Then dry with a paper towel. You can use soap on the outside and the handle. The only thing to avoid at all is acidic food like tomatoes that will rapidly remove the seasoning build-up.

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  • -1 there is no need to avoid soap or washing your pan. Obviously you want to avoid aggressive abrasive scrubbing as that will wear down the seasoning, but otherwise normal washing with hot soapy water is perfectly fine. – ljden Oct 7 '20 at 8:59
  • If soap effects your 'seasoning' then you haven't built up a true polymerised seasoning and you just have a greasy pan – ljden Oct 7 '20 at 9:00
  • I beg to disagree: it is the presence of grease gradually burning itself onto the surface of the pan than creates the non stick layer. Washing the pan with soap slows the process down. Once your pan is well blackened then you can wash it with more confidence. – Moscoffier Oct 7 '20 at 9:09
  • The seasoning process formes a polymerised layer which is essentially a plastic. Standard dish soap used today will not affect this polymer and will only break down lipids (fats). The misnomer of not using soap used to be valid as the lye in soap wpuld break down the polymers, but soap these days has no lye, and is no where near as harsh and therefore don't effect a true seasoning layer – ljden Oct 7 '20 at 9:22

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