Is Flaxseed Oil The Ultimate Way to Season Cast Iron?

There are thousands of websites out there with details and instructions on how to properly season your cast iron cooking implements. Sadly, very few, if any, actually discuss the science behind what is going on or why one method is better than another. All of them typically reference dozens of oils and fats that should or shouldn’t be used with little or no justification for their choices other than the culinary equivalent of old wives tales.

Flaxseed Oil for Seasoning Cast Iron

About two seasonings ago, I had come across an interesting concept surrounding flaxseed oil and have always meant to try it, but wanted to do some tests and comparisons of my own. After some research, I’ve found Sheryl Canter’s original article which now seems to be referenced by most serious food blogs and sites. I’ll try some tests with in the coming weeks and hopefully get around to reporting some of the results. Time to get the trusty microscope out for some photomicrography!

In the meanwhile, here are some links to what appear to be the forefront of material out there on the subject.

Original article: Chemistry of Cast Iron Seasoning: A Science-Based How-To via Sheryl Canter

Canter’s initial foray into cleaning and re-seasoning cast iron: Perfect Popovers (& How to Clean & Reseason Cast Iron)

Supporting Ideas and Criticism:

Cooks Illustrated tests: The Ultimate Way to Season Cast Iron – How To Cook – Cook’s Illustrated

LifeHacker article with references to pros and cons: Season Cast Iron Cookware with Flax Seed Oil for a Long-Lasting, Gorgeous Coat

Chow Hound discussion with pros and cons as well as criticism on the science

Harold McGee on Cast Iron

The inimitable McGee has relatively little to say on the subject, so I’ll quote it briefly below:

IRON AND STEEL

Iron was a relatively late discovery because it exists in the earth’s crust primarily in the form of oxides, and had to be encountered in it’s pure form by accident, perhaps when a fire was built on an outcropping of ore. Iron artifacts have been found that date from 3000 BCE, though the Iron Age, when the metal came into regular use without replacing copper and bronze (a copper-tin alloy) in preeminence, is said to begin around 1200 BCE. Cast iron is alloyed with about 3% carbon to harden the metal, and also contains some silicon; carbon steel contains less carbon, and is heat-treated to obtain a less brittle, tougher alloy that can be formed into thinner pans. The chief attractions of cast iron and carbon steel in kitchen work are their cheapness and safety. Excess iron is readily eliminated from the body, and most people can actually benefit from additional dietary iron. Their greatest disadvantage is a tendency to corrode, though this can be avoided by regular seasoning (below) and gentle cleaning. Like aluminum, iron and carbon steel can discolor foods. And iron turns out to be a poorer conductor of heat than copper or aluminum. But exactly for this reason, and because it’s denser than aluminum, a cast iron pan will absorb more heat and hold it longer than a similar aluminum pan. Thick cast iron pans provide steady, even heat.

“Seasoning” Cast Iron and Carbon Steel Cooks who appreciate cast iron and carbon steel pans improve their easily corroded surface by building up an artificial protective layer. They “season” them by coating them with cooking oil and heating them for several hours. The oil penetrates into the pores and fissures of the metal, sealing it from the attack of air and water. And the combination of heat, metal, and air oxidizes the fatty acid chains and enourages them to bond to each other (“polymerize”) to form a dense, hard, dry layer (just as linseed and other “drying oils” do on wood and on painintgs). Highly unsaturated oils — soy oil, corn oil — are expecially prone to oxidation and polymerizing. To avoid removing the protective oil layer, cooks carefully clean seasoned cast iron pans with mild soaps and dissolving abrassive like salt, rather than with detergents and scouring pads.

Harold McGee (1951- ), food science writer
in On Food and Cooking: The Science and Lore of the Kitchen (Scribner, revised edition 2004)

It’s almost immediately apparent that Canter was inspired to use flaxseed oil by the standard go-to reference which mentions “linseed and other ‘drying oils'”. Since it’s somewhat illustrative of cast iron pans in general, though it doesn’t reference seasoning, I’ll also direct the reader to McGee’s article What’s Hot, What’s Not, in Pots and Pans (New York Times, October 7, 2008) as well as Dave Arnold’s article Heavy Metal: the Science of Cast Iron Cooking.

I’ll note that the Culinary Institute of America’s The Professional Chef (Wiley, 7th edition, 2001) only mentions cast iron in passing on page 91 and doesn’t even use the word seasoning. (There is a more recent 9th edition, which I don’t own, but I doubt it has additional information given the scant nature found in the 7th edition.) Similarly “Iron Chef” Alton Brown’s I’m Just Here for the Food (Stewart, Tabori & Chang, 2011) has some generally fine directions for the beginning chef interested in science, but it doesn’t go past either McGee or the bulk of the online blogs with the common wisdom for cast iron.

A well-seasoned (manteca) cast iron pan cooking hashbrowns

In the coming research, I’ll delve into some of the journal literature to see what else I come up with, though I expect that it will be scant at best and not much more than the often cited July 1986 study in the Journal of the American Dietetic Association which discusses iron leaching out of pans into food substances.

Anyone with serious thoughts and ideas in this area is encouraged to share them in the comments.