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Food Science

Periodic Graphics

Periodic Graphics: The chemistry of cast-iron cookware

Chemical educator and Compound Interest blogger Andy Brunning explores how the seasoning process makes cast-iron pans nonstick.

by Andy Brunning, special to C&EN
March 25, 2024 | A version of this story appeared in Volume 102, Issue 9
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A three-column infographic highlighting the chemistry of cast-iron cookware.
Food sticks to pans because chemical bonds form between the food and the pan surface. Foods high in protein are particularly susceptible to sticking to pans because the proteins form complexes with metal atoms in cookware.
Cast-iron pans are made from an alloy of iron, carbon, and silicon. These pans owe their nonstick properties to the seasoning process, which involves applying a thin layer of oil to the pan and baking it in an oven at high temperature several times.
The thin layer of oil polymerizes in the high temperature. The polymerized oil layer stops food from sticking by making the surface of the pan smoother and repelling water.
Triglycerides in oil contain fatty acids, which have long hydrocarbon chains. At the high temperature used for pan seasoning, the hydrocarbon chains break down. The carbon-carbon double bonds in the chains polymerize to form large and complex polymer molecules that stick to the pores and crevices in the pan.
Oils high in unsaturated fats contain more carbon-carbon double bonds and polymerize more easily.
Washing cast-iron pans with dish soap doesn’t damage the polymerized seasoning.

Credit: Andy Brunning

Test your knowledge of the chemistry of cast-iron cookware with our quiz.

To download a pdf of this article, visit cenm.ag/castiron.

References used to create this graphic:

Arnold, Dave. “Heavy Metal: The Science of Cast Iron Cooking.” Cooking Issues (blog), Feb. 16, 2010.

Gao, Chenxi, Na Yang, Cunpu Li, Xi Wang, Xun Yu, Ling Zhang, and Zidong Wei. “Seasoning Chinese Cooking Pans: The Nanoscience behind the Kitchen God’s Blessing.” Nano Mater. Sci.(2023). DOI: 10.1016/j.nanoms.2020.06.001.

Royal Society of Chemistry. “Kitchen Chemistry: Why Do Pans Stick?” July 5, 2018.

Zamieroski, Kirk, writer/producer, and Adam Dylewski, executive producer. “Let’s Settle This! How to Care for Cast-Iron.” Reactions, Dec. 5, 2016. Video, 3:20.

A collaboration between C&EN and Andy Brunning, author of the popular graphics blog Compound Interest

To see more of Brunning’s work, go to compoundchem.com. To see all of C&EN’s Periodic Graphics, visit cenm.ag/periodicgraphics.

CORRECTION

This graphic was updated on Sept. 24, 2024, to correct the attribution of cast-iron pans’ nonstick properties. While some authors believe the polymerized layer makes the pan nonstick, researchers have not definitively proved this.

 

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