Don't go above the smoke point!
Recently I was getting ready for a relaxing evening of seasoning several pieces of cast iron cookware, using the Lodge instructions with canola or vegetable oil. I thought I had some canola oil in the pantry, but I didn't. All I had was (unrefined!) coconut oil. In researching if/how to do this, I found the first article in the appendix below, and I'm glad that happened, as it led me on a wondrous journey of discovery.
It's a cliche that there are a lot of opinions about seasoning cookware. Wow is that true - there is very little consensus on a standard approach. Different oils, temperatures, times, goals.
The primary shocking revelation and the reason I am writing this blog post
When seasoning cookware, one should not use heat that is above the smoke point of the oil.
How to pick an oil (probably)
- higher smoke point
- less saturated
- less flavor is better
- less fibers is better
Read on for why...
- The goal is oil polymerization
- Polymerization happens below the smoke point
- There is no reason to go above the smoke point
- We want to get hot enough to facilitate polymerization, but we do not want to go above the smoke point of the oil, because then it will burn and not polymerize
- this is very rarely stated, even in theoretically reliable sources such as Lodge's own recommendations
- Oils polymerize at any heat below the smoke point (e.g. paintings made with oil paints "dry" over the course of years at room temperature). The hotter, the faster.
- Unsaturated fats polymerize more quickly than saturated fats
- some guides say that in order to achieve polymerization, we must go above the smoke point - I believe these are clearly wrong
- a couple guides, probably overlapping with the above, say: we want both polymerization and burning, because the black ash is part of the finish we are going for
- other guides respond: we don't want to do that, people who want to do that are only going for aesthetics. oddly, some of these same guides which warn against burning do not suggest to pick your temperature based on the smoke point of your oil
- I've only seen one guide (linked below, although I think it's content farmed from some unknown original article) out of dozens which explicitly says to pick your temperature based on the smoke point of your oil, and to stay below it. The second link below says to stay "at or below" - i think "at" is risky.
- Other guides say things which support this, but don't explicitly say this. I really can't emphasize enough how there are many very long elaborate guides, which even talk about the importance of a high smoke point, but do not specify that you should keep your temperature below the smoke point.
- Flaxseed oil was in vogue for a while, and now some people are saying it flakes after a while. It has a very low smoke point of 225! So I suspect people using it, while using typical temps of 450, are putting on tons of layers of ash - it looks great but doesn't actually result in much polymerization.
- Grapeseed oil seems to be an emerging favorite. I wonder if part/much of this is because it has a higher smoke point than Canola oil, so people are accidentally achieving less burning (if using same temp for both).
- some oils have fibers, which creates a lower smoke point. so, even if other things are equal (such as the polymerized oil being just as good for any oil), the presence of fibers is probably bad, because after seasoning, they will burn during cooking (although maybe this will be very fast and minor). A higher smoke point probably generally correlates with fewer fibers. So higher smoke point oils could be preferable for (at least) this reason.
- The presence of flavor implies the presence of non-oil compounds, and we probably want as much oil as possible and nothing else, so a less-flavorful oil is probably preferable for this reason.
- Lodge uses soybean oil in their factory
- Lodge seasoning spray that they sell to you is 100% canola oil
- You can also season other types of cookware, such as aluminum baking sheets and muffin pans (which I have done with good initial results), and carbon steel, using the same method. People also talk about seasoning stainless steel. I think the seasoning won't stick as well to this shiny surface but I haven't tested it.
- After different oils polymerize fully, do they have differnt attributes?
- max heat
- how long does it really take for the thin layer of oil to fully polymerize? Does this differ significantly by oil?
My method for now
I've done 3 layers with coconut oil at 325 and it looks fantastic and to my eye seems pretty non-ashy. Don't know how it performs yet.
My experiments so far were pretty inconsistent because I was researching and doing it at the same time so I used different temps and durations in different phases.
Going forward, I'm going to use avocado oil at a higher temp (well below smoke point).
If the theory that the temp doesn't need to be super high to have good polymerization is correct, that could make the process more convenient- it's more convenient to work with 350F vs 450F+ as items go in and out of the oven.
- https://www.castironcollector.com/seasoning.php (i discovered this after my initial research and while writing this - i didn't read it carefully yet, will do so eventually)
- https://chemistry.stackexchange.com/questions/169685/after-an-oil-polymerizes-what-is-its-smoke-point (in typical SE fashion, downvoted but still useful almost-answers in the comments )
- Lodge Factory: https://www.youtube.com/watch?v=NEQP94YbYFo
Thanks to Zachary Hudson, Associate Professor at The University of British Columbia Department of Chemistry, for answering a couple questions!