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cast iron: polymerizing oils and a better seasoning

paul wheaton — Tue, Mar 2 2010 09:08:41 MST

From a different thread, I wrote the following:

Linseed (flax) oil is kinda famous for becoming rancid quickly. And, so, you're saying that it is also indicative that it is quick to polymerize.

Grape seed oil has a similar reputation.

So it seems there is at least a mild challenge of getting the oil from the plant into the bottle and from the bottle into my pan. Just simple storage can be tricky. ??

So, at cooking temperatures, any oil will polymerize, right? And then it doesn't really matter which one does it at the lowest temperature, but which one will do it more evenly and result in a slipperier surface.

In fact, we might end up with different fats that polymerize in different ways. Some might leave a super slippery surface, but be poor for the first layers on iron. Some might help fill in a pit or fill in a rough (new lodge) surface.

I know that I have had times where fats will leave a polymerized layer that is a thin, contiguous layer. And other times where fats will leave a layer that is "mottled" or "spider-web-ish". I suspect that there are a lot of factors here, one of which could be the different types of oils. It might even be compounded with the type of oil/layer from the previous use of the pan.

I guess my point is that it is results that count. And the real results would be to try a dozen different types of fat cooking the same thing five times in a row and to conclude which was the best on the fifth time.

First, I am seeking validation that while linseed (flax) oil may be good for .... uh .... painting/staining a piece of furniture because that piece of furniture will not be exposed to high temps, that it doesn't necessarily make it a great candidate for seasoning cast iron. Can I get agreement on that? Is my thinking sound?

Next, I think it may be wise to caution people against the use of linseed oil because I think it might have chemicals added - even if the label says it does not have chemicals added. Refrigerated flax seed in a dark bottle might be a much better choice.

And finally .... and this, I think, is the most important thing: what might be the combination of oil of temp to get a hard contiguous layer of polymerized oil as opposed to the "mottled" or "webby" layer that I usually see in a secondary seasoning layer?

Re: cast iron: polymerizing oils and a better seasoning

paul wheaton — Tue, Mar 2 2010 09:09:59 MST

And while we're on the subject .... I would really like to better understand the free radical stuff.

Re: cast iron: polymerizing oils and a better seasoning

Sheryl Hatfield — Tue, Mar 2 2010 10:27:43 MST

Of course you want to use food-grade flaxseed oil (from a health food store), not the linseed oil that a hardware store sells.

I've only seen the "webby" thing when I used bacon fat, and I think that happened because there are non-oil things in it - salt, notably, and who knows what else.

"Free radicals" have to do with molecular chemistry - unstable molecules emitting electrons until they are stable. It's a chemical reaction that causes the molecule to change into something else.

Re: cast iron: polymerizing oils and a better seasoning

Jami McBride — Tue, Mar 2 2010 13:30:15 MST

Paul, after reading/following your cast iron thread I was still using a sticking cast iron skillet, I don't know what I was doing different than others, but I tried everything.

I followed the link you posted to Sheryl's Blog - The article titles are at the end of these URL's
http://sherylcanter.com/wordpress/2010/01/a-science-based-technique-for-seasoning-cast-iron/
http://sherylcanter.com/wordpress/2010/02/black-rust-and-cast-iron-seasoning/

I followed her directions and now have the nicest, slick black finish on my pans ever! They look better than they did when purchased, and we are making pancakes again for the first time in years.... I'm a happy camper to say the least.

I used the health store flax seed oil - it works great. I do not see why you are having trouble excepting it's use for this purpose. I now love cooking with my cast iron, but most important I'm not afraid to use it, I know I can easily re-season it should the need ever pop up again.

By the way that's coconut oil in the jar next to the pan, we don't use flax seed oil for cooking just seasoning.

Re: cast iron: polymerizing oils and a better seasoning

Sheryl Hatfield — Tue, Mar 2 2010 13:33:36 MST

That is awesome to hear. Thank you for posting this! (I'm Sheryl.)

Re: cast iron: polymerizing oils and a better seasoning

Jami McBride — Tue, Mar 2 2010 19:47:59 MST

Your most welcome Sheryl

~Jami

Re: cast iron: polymerizing oils and a better seasoning

paul wheaton — Fri, Mar 5 2010 10:18:42 MST

Sheryl,

Perhaps the point is that the flax oil will polymerize before the smoke point? Or, maybe the polymerization would happen without the webbiness?

But then it would seem that the corollary would be that you would want to not use flax oil for general cooking - because then you would be eating a lot of polymerized oils. ??

Re: cast iron: polymerizing oils and a better seasoning

Kerrick McCoy — Fri, Mar 5 2010 12:01:18 MST

You don't want to use flax oil for cooking; you want to eat it raw. At least that's what I've always heard--and the folks I know who are serious about their flax keep it in the refrigerator, or even in the freezer. I gathered from that blog post (REALLY informative, btw, thanks Jami and Sheryl!) that the smoke point for flax IS the polymerization point, so you most certainly do not want to heat it very much, if at all.

I'm going to try stripping mine and replacing the seasoning with flax oil sometime next week; I'll report back on how it works.

Re: cast iron: polymerizing oils and a better seasoning

Jami McBride — Fri, Mar 5 2010 13:23:34 MST

Exactly Kerrick you've got it!

Buy the way, those pancakes are from the Nourishing Traditions Cook Book and use wheat flour soaked in liquid yogurt overnight before cooking the next day - boy were they goooood!

Re: cast iron: polymerizing oils and a better seasoning

Sheryl Hatfield — Sat, Mar 6 2010 06:36:39 MST

You never ever never want to use flax oil for cooking. Polymerization is for the pan, not for inside your body. Free radicals inside your body are known to be carcinogenic. The smoke point is the point at which the free radicals are released. Flaxseed oil has a very low smoke point. Never cook with it, and keep it in the refrigerator.

Re: cast iron: polymerizing oils and a better seasoning

Jami McBride — Sat, Mar 6 2010 12:39:14 MST

Sheryl,

Is this smoke-point free-radicals thing true for all oils?

And if so is there are chart showing the smoke point temps for various oils?

Thanks

Re: cast iron: polymerizing oils and a better seasoning

Ken Peavey — Sat, Mar 6 2010 14:15:56 MST

from http://www.cookingforengineers.com/

Fat                              Smoke Point     °F           °C
Unrefined canola oil                          225°F	107°C
Unrefined flaxseed oil                     	 225°F	107°C
Unrefined safflower oil	                 225°F	107°C
Unrefined sunflower oil                     225°F	107°C
Unrefined corn oil                             320°F	160°C
Unrefined high-oleic sunflower oil	 320°F	160°C
Extra virgin olive oil	                         320°F	160°C
Unrefined peanut oil	                 320°F	160°C
Semirefined safflower oil	                 320°F	160°C
Unrefined soy oil	                         320°F	160°C
Unrefined walnut oil	                         320°F	160°C
Hemp seed oil	                                 330°F	165°C
Butter	                                         350°F	177°C
Semirefined canola oil	                 350°F	177°C
Coconut oil	                                 350°F	177°C
Unrefined sesame oil	                 350°F	177°C
Semirefined soy oil	                         350°F	177°C
Vegetable shortening	                 360°F	182°C
Lard	                                                 370°F	182°C
Macadamia nut oil	                         390°F	199°C
Refined canola oil	                         400°F	204°C
Semirefined walnut oil	                 400°F	204°C
High quality (low acidity) extra virgin olive oil	405°F	207°C
Sesame oil	                                 410°F	210°C
Cottonseed oil	                                 420°F	216°C
Grapeseed oil	                                 420°F	216°C
Virgin olive oil	                                 420°F	216°C
Almond oil	                                 420°F	216°C
Hazelnut oil	                                 430°F	221°C
Peanut oil	                                         440°F	227°C
Sunflower oil	                                 440°F	227°C
Refined corn oil	                         450°F	232°C
Refined high-oleic sunflower oil	 450°F	232°C
Refined peanut oil	                         450°F	232°C
Refined Safflower oil	                 450°F	232°C
Semirefined sesame oil	                 450°F	232°C
Refined soy oil	                                 450°F	232°C
Semirefined sunflower oil	                 450°F	232°C
Olive pomace oil	                         460°F	238°C
Extra light olive oit	                         468°F	242°C
Soybean oil	                                 495°F	257°C
Safflower oil	                                 510°F	266°C
Avocado oil	                                 520°F	271°C

There is also a chart on wikipedia

Re: cast iron: polymerizing oils and a better seasoning

Sheryl Hatfield — Sat, Mar 6 2010 16:53:52 MST

Thanks for posting the chart, Ken. That's where I found it, too.

Yes, Jami, the smoke point for any oil is when it starts to release free radicals. That's why you never should heat oil for cooking so hot that it smokes, and if you do it by accident you should throw it away (unless you're seasoning a cast iron pan, of course).

The reason this chart was posted on Cooking for Engineers is so people would know which oils were safe for cooking and which were not. Here's the beginning of that article:

http://www.cookingforengineers.com/article/50/Smoke-Points-of-Various-Fats

The smoke point of various fats is important to note because a fat is no longer good for consumption after it has exceeded its smoke point and has begun to break down. Once a fat starts to smoke, it usually will emit a harsh smell and fill the air with smoke. In addition it is believed that fats that have gone past their smoke points contain a large quantity of free radicals which contibute to risk of cancer.

Re: cast iron: polymerizing oils and a better seasoning

wombat McCoy — Sun, Mar 14 2010 16:23:33 MDT

http://www.permies.com/permaculture-forums/3496_0/cooking-and-food-preservation/black-residue-on-cast-iron-skillet

I was so inspired by Pauls article on cleaning cast iron pans that I spent most of the day cleaning up my old iron Ive collected over the years. I posted at the link.

I have been using a spray can of canola oil (PAM) which I just happened to have on hand, with coarse salt after the pan is heated and scraped down.

According to Ken's chart refined canola oil should have a smoke point of 400 degrees F. The method I am using heat + scraping or wire brushing, and then a final rub down with just a spritz of oil on a paper towel with salt means that with each use the old oil is replaced with fresh oil so carcinogens should never form. You could use lard the same way -- just a dab of fresh lard after each use.

Re: cast iron: polymerizing oils and a better seasoning

paul wheaton — Sat, Mar 20 2010 05:55:57 MDT

I'm trying to eliminate all soy oil and canola oil from my diet. But, that's just me. The mention of canola oil made me think of mentioning that.

Re: cast iron: polymerizing oils and a better seasoning

wombat McCoy — Sat, Mar 20 2010 08:42:01 MDT

Why? Why eliminate soy and canola oils? I used canola oil thinking it had a higher smoking point -- and I had some on hand because I was using it to remove rust from my tools. It comes in a spray can just like WD40 (!)

According to the chart olive oil - which I more normally have in my kitchen has a higher smoking point. I guess peanut oil would be a better frying oil.

Re: cast iron: polymerizing oils and a better seasoning

Wendell McCoy — Mon, Dec 27 2010 06:09:53 MST

I have just seasoned three Griswolds and an unknown no. 12 using flaxseed oil, and now have four beautiful skillets eager to be used.

However, because of a severe headache during the seasoning process, I began to wonder about the health risks associated with cooking on a flaxseed glaze. I read that flaxseed oil must not be used for cooking. If any of the seasoning layer comes off in using the pan, isn't that adding cooked flaxseed oil to our food? Maybe the polymerization process eliminated any of the harmful agents (free radicals).

Will my pans smoke when I put them onto the fire (I'll find that out soon enough!). If they initially smoke, will that diminish in time?

In seasoning, I ran my oven temperature as high as 550 degrees and held them over 400 for an hour. With four cast iron pans in the oven, it held heat for about three hours before the pans were cool enough to handle. Because of this health question I stopped the process after the fifth baking cycle. I started by sand blasting down to bare metal and re-polishing the inside with a wire wheel. They are a beautiful deep, dark coppery color.

Re: cast iron: polymerizing oils and a better seasoning

Sheryl Hatfield — Mon, Dec 27 2010 09:35:38 MST

Any smoking oil will give you a headache. You need very good ventilization when you do this. Once the polymerization is complete, the surface won't smoke.

Re: cast iron: polymerizing oils and a better seasoning

Rob Sigg — Thu, Dec 30 2010 10:41:40 MST

This is a great post because I believe it identifies the real issue to heart/cardiovascular issues not cholesterol. I use a cast iron pan and it is awesome, I will have to learn more about the polymerizing of the pan, this is new to me.

Re: cast iron: polymerizing oils and a better seasoning

paul wheaton — Mon, Sep 5 2011 17:01:37 MDT

Jocelyn shows us how to put a new seasoning layer on a funky old

Re: cast iron: polymerizing oils and a better seasoning

Rob Sigg — Thu, Sep 8 2011 18:28:12 MDT

Nice video, and great info!

Re: cast iron: polymerizing oils and a better seasoning

The Dirt Surgeon — Fri, Sep 9 2011 13:24:51 MDT

Am I the only person to use bacon grease? It never smokes at the temperatures I use, and it's absolutely free because I've already bought the bacon! And the delicious bacon flavor... mmmm.

Well, there's a health issue, I'm sure someone will say... my grandma used bacon grease all her life, and it killed her early, at the tender young age of 96.

Veg and seed oils frighten me a bit, considering there's no way of knowing where they come from. Then stuff in spray cans... seriously? That's creepy, not to mention a waste of resources in the form of that can you throw away. What if you accidentally grab the Liquid Wrench, cooking breakfast some dark morning?

Re: cast iron: polymerizing oils and a better seasoning

Rob Sigg — Fri, Sep 9 2011 13:28:40 MDT

Lard and bacon fat are our staples. Occasionaly we use some coconut oil too.

Re: cast iron: polymerizing oils and a better seasoning

Alex Ojeda — Wed, Sep 21 2011 05:48:48 MDT

Personally, I've eliminated all oils that have a GMO equivalent in the marketplace. The cross contamination has made even organic foods "iffy". Even organic farmers can't promise that you aren't getting GMO content in their foods.

Mainly for health and partly because it seems like a protest or a boycott. I consider GMO foods to be the bane of all life on this planet and the first and most important evil on my list of things to concentrate on changing.

I really hope that everyone will look into this issue and determine for themselves if I'm crazy or not

wombat wrote:
Why? Why eliminate soy and canola oils? I used canola oil thinking it had a higher smoking point -- and I had some on hand because I was using it to remove rust from my tools. It comes in a spray can just like WD40 (!)

According to the chart olive oil - which I more normally have in my kitchen has a higher smoking point. I guess peanut oil would be a better frying oil.

Re: cast iron: polymerizing oils and a better seasoning

Erik Lee — Fri, Sep 23 2011 13:25:35 MDT

Grassfed beef tallow is my staple pan seasoner. It seems to make a bulletproof nonstick coating that lasts a good long time.

On the soybean oil issue, I eliminated it from my repertoire as well, primarily because of the horrible extraction process required to get the oil out of the seed (involves hexane, high temperatures, alkaline washes, and various other industrial processes that I don't want to eat). Also, the omega-3/6 balance is way out of whack, which is believed by many to be a factor in various "diseases of civilization."

It costs a lot more, but I try to stick to extra-virgin oils or animal fats that I render myself from animals I know were raised in conditions they are adapted to. I think that once you get past the virgin oil level, many of the vegetable oils have been processed with crazy chemicals, and undergone oxidizing transformations that may contribute to atherosclerosis.

cast iron: polymerizing oils and a better seasoning

Craig Storms — Thu, Sep 20 2012 10:09:19 MDT

Chemistry of Cast Iron Seasoning: A Science-Based How-To

Chemistry of Cast Iron Seasoning: A Science-Based How-To
January 28, 2010, 6:31 pm
The post after this one on “black rust” describes why you should heat the pan before applying oil for seasoning. This helps the seasoning to adhere and makes the pan pleasantly black.

http://sherylcanter.com/wordpress/2010/02/black-rust-and-cast-iron-seasoning/

In a previous post, I illustrated how I cleaned and reseasoned an antique cast iron popover pan. This was my first attempt, and my seasoning technique was somewhat haphazard because I couldn’t find consistent, science-based advice. I used a combination of organic avocado oil and strained drippings from organic bacon. This worked pretty well on the popover pan, which doesn’t have a polished surface. But the smooth inner surface of a skillet showed an unevenness of color and texture, and the seasoning wasn’t hard enough. It was too easily marred by cooking utensils or scraping against oven racks.

I wanted to understand the chemistry behind seasoning so I’d know how to fix this, but there is nothing that addresses this issue directly. A Web page on cast iron posted by someone similarly obsessed with the science gave me two crucial clues, the phrases “polymerized fat” and “drying oil”. From there I was able to find the relevant scientific literature and put the pieces together.

http://sherylcanter.com/wordpress/2010/01/a-science-based-technique-for-seasoning-cast-iron/?roostBDI=375678

cast iron: polymerizing oils and a better seasoning

Keith Williams — Tue, Oct 30 2012 21:49:21 MDT

Craig Storms wrote:Chemistry of Cast Iron Seasoning: A Science-Based How-To
Chemistry of Cast Iron Seasoning: A Science-Based How-To
I wanted to understand the chemistry behind seasoning so I’d know how to fix this, but there is nothing that addresses this issue directly. A Web page on cast iron posted by someone similarly obsessed with the science gave me two crucial clues, the phrases “polymerized fat” and “drying oil”. From there I was able to find the relevant scientific literature and put the pieces together.
http://sherylcanter.com/wordpress/2010/01/a-science-based-technique-for-seasoning-cast-iron/?roostBDI=375678

A lot of people quote from and link to this article from Sheryl, but I have never seen Sheryl post anything scientific about how she came up with her method other than mentioning the keyword of polymerization. I think that cast iron seasoning might have more to it chemistry-wise than just a polymerization of oils. I have posted my thoughts at http://www.reddit.com/r/askscience/comments/12c42u/what_is_cast_iron_seasoning_really_made_of/

Basically, I think that cast iron seasoning might be a combination of a polymerized layer working together with oils that have saponificated (turned to soap) and/or soap that has mixed with oil to become grease. Paul's long post on richsoil.org about how to use cast iron without worrying about it too much along with using a straight edged stainless steel spatula / pancake flipper are what got me thinking about this theory.