You are here:

Chemistry (including Biochemistry)/Flax oil to season cast iron?


I've been following advice on the internet to treat my cast iron pans with flax oil. Apparently it heats to a hard finish which makes cleaning the pans easy. But, since flax oil goes rancid so quickly and isn't supposed to be heated I'm worried that every time I cook with the pans I will be poisoning our food.

I've got the pans all stripped and scrubbed and ready to treat. What do you think I should do?

Hello D'arcy!

Short answer: You should be fine. Open the windows and go start your pans seasoning. Then come back and read the rest.

Longer answer: You should be fine.

Rancidity in and of itself tastes yucky but isn't necessarily toxic. We say oils have gone rancid when free radicals (think streaking electrons) are traveling willy-nilly through the oil. When a naked electron hits a carbon-carbon or carbon-oxygen double bond, there's a good chance that the naked electron will end up breaking that molecule apart into smaller pieces. This can produce weird odors and funky smells.

Flaxseed oil has lots of molecules with these double bonds, so it is easy for the flaxseed oil to go rancid on you. (Hence expense and careful storage.)

Now when you follow the above process and season your cast iron six times (Oh my!) at high heat, you are actually doing something a little bit different to all those double bonds. Instead of hitting them willy nilly with random electrons, you're heating up the molecules to the point where the double bonds are more likely to wiggle themselves open on their own. At this point a flaxseed oil molecule will notice its neighbor, who has its double bonds open too, and is very likely to form a cross-bond with the neighbor. Repeated instances of this result in polymerization of the oil, which is what makes for the nice glossy finish. We want the oil coat on the iron to be thin so that all the double bonds get heated open, interact with the iron and the air, and polymerize. :)

When your flaxseed oil molecules are all bound up with their neighbors holding hands on top of the iron base, they cannot go rancid. They've already given up their double bonds, so if random streaking electrons happen they will find no 'interesting' double bonds to 'play' with and break apart.

If you just heated a lot of the oil on your stovetop, however, there would not be enough iron or enough air, and instead of polymerizing the oil would break apart and smell funny. Hence, don't use flaxseed oil for cooking. :)

Let me know if you have any more questions! This was a cool topic to look in to. :)

Chemistry (including Biochemistry)

All Answers

Answers by Expert:

Ask Experts


Trista Robichaud, PhD


No homework questions, especially ones copied and pasted from textbooks. I will answer questions about principles or give hints, but I do not do other's homework. I'm comfortable answering basic biochemistry, chemistry, and biology questions up to and including an undergraduate level of understanding. This includes molecular biology, protein purification, and genetics. My training/inclination is primarily in structural biology, or how the shapes of things affect their function. Other interests include protein design, protein engineering, enzyme kinetics, and metabolic diseases such as cancer, atherosclerosis, and diabetes. My chemistry weaknesses are that I do not know organic or inorganic synthesis well, nor am I familiar with advanced inorganic reactions. I will attempt quantum mechanics and thermodynamics questions, but primarily as they relate to biological systems. Furthermore, I cannot tell you if a skin photograph is cancerous, or otherwise diagnose any disease. I can tell you how we currently understand the basic science behind a disease state, but I cannot recommend treatment in any way. Please direct such questions to your medical professional.


I hold a PhD in Biomedical Science from the University of Massachusetts Medical School in Worcester. I specialize in Biochemistry, with a focus on protein chemistry. My thesis work involved the structure and functions of the human glucose transporter 1. (hGLUT1) Currently I am a postdoc working in peptide (mini-protein) design and enzymology at the University of Texas Health Science Center in San Antonio, Texas. I am in Bjorn Steffensen's lab (PhD, DDS), studying gelatinase A and oral carcinoma.

2001 American Association for the Advancement of Science
2007 American Chemical Society
2007 Protein Society
2011 UTHSCSA Women’s Faculty Association

Levine KB, Robichaud TK, Hamill S, Sultzman LA, Carruthers A. Properties of the human erythrocyte glucose transport protein are determined by cellular context. Biochemistry 44(15):5606-16, 2005. (PMID 15823019)
Robichaud TK, Appleyard AN, Herbert RB, Henderson PJ, Carruthers A “Determinants of ligand binding affinity and cooperativity at the GLUT1 endofacial site” Biochemistry 50(15):3137-48, 2011. (PMID 21384913)
Xu X, Mikhailova M, Chen Z, Pal S, Robichaud TK, Lafer EM, Baber S, Steffensen B. “Peptide from the C-terminal domain of tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) inhibits membrane activation of matrix metalloproteinase-2 (MMP-2)” Matrix Biol. 2011 Sep;30(7-8):404-12. (PMID: 21839835)
Robichaud TK, Steffensen B, Fields GB. Exosite interactions impact matrix metalloproteinase collagen specificities. J Biol Chem. 2011 Oct 28;286(43):37535-42 (PMID: 21896477)

Poster Abstracts:
Robichaud TK, Carruthers. A "Mutagenesis of the Human type 1 glucose transporter exit site: A functional study." ACS 234th Meeting, Boston MA. Division of Biological Chemistry, 2007
Robichaud TK, Bhowmick M, Tokmina-Roszyk D, Fields GB “Synthesis and Analysis of MT1-MMP Peptide Inhibitors” Biological Chemistry Division of the Protein Society Meeting, San Diego CA 2010
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Catalytic Domain Exosites Contribute to Determining Matrix Metalloproteinase Triple Helical Collagen Specificities” Dental Science Symposium. UTHSCSA 2011
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon Research Conference on Matrix Metalloproteinase Biology, Bristol RI 2011

Oakland University, Auburn Hills MI BS, Biochemistry 1998
University of Massachusetts Medical School, Worcester MA PhD, Biochemistry & Molecular Pharmacology 2001-2008
University of Texas Health Science Center, San Antonio TX Postdoc, Biochemistry 2009-Present

Awards and Honors
1998 Honors College Graduate, Oakland University
2009 Institutional National Research Service Award, Pathobiology of Occlusive Vascular Disease T32 HL07446
2011 1st Place, Best Postdoctoral Poster, Dental Science Symposium, UTHSCSA, April 2011

Past/Present Clients
Invited Seminars:
Robichaud TK, Fields GB. “Synthesis and Analysis of MTI-MMP Triple Helical Peptide Inhibitors” Pathology Research Conference, University of Texas Health Science Center San Antonio Pathology Department (June 18th, 2010)
Robichaud TK & Hill, B “How To Give A Great Scientific Talk” Invited Lecture, Pathobiology of Occlusive Vascular Disease Seminars, UTHSCSA (Nov 11th 2010), Cardiology Seminar Series, Texas Research Park (Feb 21st, 2011)
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon-Keenan Research Seminar “Everything You Wanted to Know About Matrix Metalloproteinases But Were Afraid to Ask” Bristol, RI (Aug 6th, 2011)

©2017 All rights reserved.