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I've a carbon steel pan that's 26 cm in diameter, about 2 mm thick, but I doubt that it matters. I haven't been able to find a reliable resource that would tell me the smoke point of flaxseed oil, but I believe it's around 180 degrees Celsius.

I pour about 5 ml of oil on the pan, rub it in every nook and cranny, and then wipe "all" the oil off with a paper towel, and stick it in the oven set to 250.

How long should I keep the oven on? People have differing opinions on that; one says an hour, other 30 minutes, and I've even seen someone say 15 minutes.

I've done some field testing, and I nowadays burn the pan for 30 minutes, but I wonder if I could go lower. It's not just a matter of testing it, as a bad layer ruins the pan, it will flake and has to be sanded, and burnt at least 3 times after that.

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  • $\begingroup$ You might get more traction on this on our sister site Seasoned Advice (cooking and related). $\endgroup$ – Todd Minehardt Apr 30 at 17:45
  • $\begingroup$ I think that site will get me biased answers. I want the science behind it. $\endgroup$ – user465789 Apr 30 at 18:03
  • $\begingroup$ I doubt you'll get anything else here. Quantitative scientific measures on the seasoning are hard to get. It's so thin and largely amorphous ... I never bothered about old layers, though. Does it make a difference if you remove them? $\endgroup$ – Karl Apr 30 at 18:22
  • $\begingroup$ Well, I guess the most important underlying question is how long does it take for the oil to stop smoking. The layer of it is so thin that it should burn off relatively fast. The underlying layers make it better overall, it's less likely to break and it's forgiving if you scratch it. I guess it heats slightly slower with the old layers but how big of a difference can it be. $\endgroup$ – user465789 Apr 30 at 18:32
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  1. Use organic 100% flaxseed oil, unless you prefer grape seed oil.

  2. Apply the flaxseed oil to a pan preheated to 200°F.

  3. Remove all the flaxseed oil with a paper towel (some will remain).

  4. Place the dry pan in oven and heat to 500°F (or 450°F if that's as high as your oven goes) and preheat the pan with the oven.

  5. When the oven reaches temperature set a timer for one hour.

  6. After one hour turn the oven off. Leave the pan in the oven with the door closed.

  7. Wait two hours for the pan in the oven to cool.

  8. Repeat the thin oil application and baking six times.

  9. Once the pan developed a bit of a sheen it's ready.

    Always use the thinnest possible coat of oil.

References:

Science:

  • CastIronCollector.com has a science based article: "Cast Iron Seasoning" (the polymerization of the oil and it's carbonization is what's relevant, not whether the pan is cast iron or carbon steel). They recommend grape seed oil.

Note: The cooks at ChowHound disagree with Cheryl's science but are satisfied with the result. There is also some disagreement at Cooking.SE, links below.

  • Cheryl's Blog - "Chemistry of Cast Iron Seasoning: A Science-Based How-To" (Same principal as CS):

    The seasoning on cast iron is formed by fat polymerization, fat polymerization is maximized with a drying oil, and flaxseed oil is the only drying oil that’s edible.

    ...

    Fat polymerization can be triggered or accelerated in a variety of ways. As best I can tell from my reading, the cast iron seasoning process is an example of “radical polymerization”. The process is initiated when something causes the release of free radicals in the oil. The free radicals then “crosslink” to form the tough, hard film you see in a well-seasoned pan.

    So what is the “something” that initiates the release of free radicals in fat? Iron, for one thing. High heat, light, and oxygen, for some others. To prevent cooking oils from going rancid – i.e., breaking down and releasing free radicals – you need to store them in dark, tightly sealed containers in a cool location. To initiate or accelerate the release of free radicals, put the oil in contact with bare iron and heat it above its smoke point, which will cause even non-drying oils to release free radicals

    ...

    Buy an organic flaxseed oil. You don’t want to burn toxic chemicals into your cookware to leach out forever more. It’s a fairly expensive oil. I paid $17 for a 17 ounce bottle of cold-pressed, unrefined, organic flaxseed oil. As it says on the bottle, shake it before you use it.

    Strip your pan down to the iron using the techniques I describe in my popover post. Heat the pan in a 200°F oven to be sure it’s bone dry and to open the pores of the iron a little. Then put it on a paper towel, pour a little flaxseed oil on it (don’t forget to shake the bottle), and rub the oil all over the pan with your hands, making sure to get into every nook and cranny. Your hands and the pan will be nice and oily.

    Now rub it all off. Yup – all. All. Rub it off with paper towels or a cotton cloth until it looks like there is nothing left on the surface. There actually is oil left on the surface, it’s just very thin. The pan should look dry, not glistening with oil. Put the pan upside down in a cold oven. Most instructions say to put aluminum foil under it to catch any drips, but if your oil coating is as thin as it should be, there won’t be any drips.

    Turn the oven to a baking temperature of 500°F (or as high as your oven goes – mine only goes to 450°F) and let the pan preheat with the oven. When it reaches temperature, set the timer for an hour. After an hour, turn off the oven but do not open the oven door. Let it cool off with the pan inside for two hours, at which point it’s cool enough to handle.

    The pan will come out of the oven a little darker, but matte in texture – not the semi-gloss you’re aiming for. It needs more coats. In fact, it needs at least six coats. So again rub on the oil, wipe it off, put it in the cold oven, let it preheat, bake for an hour, and let it cool in the oven for two hours. The picture above was taken after six coats of seasoning. At that point it starts to develop a bit of a sheen and the pan is ready for use.

    If you try this, you will be tempted to use a thicker coat of oil to speed up the process. Don’t do it. It just gets you an uneven surface – or worse, baked on drips. Been there, done that. You can’t speed up the process. If you try, you’ll mess up the pan and have to start over.

    The reason for the very hot oven is to be sure the temperature is above the oil’s smoke point, and to maximally accelerate the release of free radicals. Unrefined flaxseed oil actually has the lowest smoke point of any oil (see this table). But the higher the temperature the more it will smoke, and that’s good for seasoning (though bad for eating – do not let oils smoke during cooking).

    I mentioned earlier there’s a myth floating around that vegetable oils leave a sticky residue. If the pan comes out of the oven sticky, the cause is one of three things:

    • You put the oil on too thick.
    • Your oven temperature was too low.
    • Your baking time was too short.

    There is also a comment section below the article.

For cooking related advice:

$$\begin{array}{lcr} \text{Fat} & \text{Quality} & & \; \text{Smoke Point} \qquad \qquad \; \\ \hline \text{Flaxseed oil} & \text{(Unrefined)} & \text{107°C} & \text{225°F} \qquad \\ \text{Lard} & & \text{190°C} & \text{374°F} \qquad \\ \text{Grape seed oil} & & \text{216°C} & \text{421°F} \qquad \\ \text{Butter} & \text{(Clarified)} & \text{250°C} & \text{482°F} \qquad \\ \text{Sunflower oil} & \text{(Neutralized)} & \text{252-254°C} & \text{486–489°F} \qquad \\ \text{Safflower oil} & \text{(Refined)} & \text{266°C} & \text{510°F} \qquad \\ \text{Avocado oil} & \text{(Refined)} & \text{270°C} & \text{520°F} \qquad \end{array} $$

Answer on Cooking.SE opposing the use of high iodine oils recommends "whatever makes a nice firm bar of soap - lard, palm oil, coconut - is a good choice here".

That answers "the science" behind seasoning, offers cooking experts advice, and says what, why and how long. Admittedly there's some disagreement. Your heat and times are too short - that is both my experience and a commonality amongst the advice offered.

Video demonstration by Chef Rich with brief scientific explanation, showing the result of coating eleven times on the stovetop using flaxseed oil. Very little smoke and very shiny black finish.

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  • $\begingroup$ The cooking SE answer that you linked. The author doesn't know what they are talking about. Recommends lard or coconut oil. My father has the same opinion; lard is best. It probably works fine for cast iron, but I tried lard once on carbon steel, and I had to sand the entire pan down because it was the worst coating I had ever seen on a pan, and it worked about as well as it looked like. And coconut oil has a smoke point so high that it doesn't even polymerize properly. $\endgroup$ – user465789 May 1 at 17:53
  • $\begingroup$ Sorry for being that guy but I've one more. That chart you got from Wikipedia. It attributes to this page, which is nowhere near credible: jonbarron.org/diet-and-nutrition/…. It's a marketing site that seems to idolize some dude called Jon Barron. It also doesn't tell how the information was obtained, and I doubt that the author poured flaxseed oil in a glass, and heated it slowly while monitoring it's temperature. $\endgroup$ – user465789 May 1 at 18:04
  • $\begingroup$ Just a brief reminder to keep it friendly in the comments, please. I think the comments above are okay because they are refuting the content and are not any type of personal attacks. $\endgroup$ – jonsca May 2 at 13:46
  • $\begingroup$ @jonsca I disagree, the statement about another SE user: "The author doesn't know what they are talking about." is in fact a personal attack and R/A - it is also unsupported by a link to an authoritative source. Badgering, berating and an unfriendly tone isn't the way to ask for clarification or improvement. That said, moderate as you see fit - I will ignore any rudeness and not respond. My "New Contributor" tag means that the experience should be better. $\endgroup$ – Rob May 2 at 13:58
  • $\begingroup$ I personally find this answer quite hand-wavy as it for my taste does not contain enough science/chemistry about what is going on on the molecular level. I also would not consider any of the sources credible enough for a scientific discourse. I presume that the seasoning of kitchenware is scientifically not-so-well explored. I am sorry that the experience is not what you have expected, I hope that does not deter you from contributing more. $\endgroup$ – Martin - マーチン May 2 at 15:13

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