Seasoned Pan

cast iron

A seasoned pan has a stick-resistant coating of polymerized fat and oil on the surface (a polymer is a molecule, made from joining together many small molecules called monomers). Seasoning is desirable on cast-iron cookware and carbon steel cookware, because otherwise they are very sticky to foods and rust-prone. For other pans (e.g., stainless, aluminum, enamelled), the same chemical phenomenon can occur, but seasoning may not be desired for cosmetic reasons (it makes a pan look splotchy), or the pan may already be stick-resistant (e.g., at medium heat, a clean stainless pan with oil is very stick resistant to many foods).

The process of heating a pan to cause the oil to oxidize is analogous to the hardening of drying oil used in oil paints, or to varnish a painting. When oils or fats are heated in a pan, multiple degradation reactions occur, including: autoxidation, thermal oxidation, polymerization, cyclization and fission.

Often seasoning is uneven in a pan, and over time the distribution will spread to a whole pan. Heating the cookware (such as in a hot oven or on a stovetop) facilitates the oxidation of the iron; the fats and/or oils protect the metal from contact with the air during the reaction, which would cause rust to form. Some cast iron users advocate heating the pan slightly before applying the fat or oil to ensure that the pan is completely dry and to open ‘the pores’ of the pan.

The surface is hydrophobic (resistant to water), and oils or fats for cooking will spread evenly. The seasoned surface will deteriorate at the temperature where the polymers breakdown. This is not the same as the smoke point of the original oils and fats used to season the pan because those oils and fats are transformed into the plasticized surface. (This is analogous to how the smoke point for crude oil and plastic are different).

A bare, unseasoned pan will need to develop a base coat of polymerized animal fat or vegetable oil. This base coat is initially created by a process of layering a very thin coat of oil on the pan. Then, the oil is polymerized to the metal’s surface with high heat for a duration. The base coat will eventually develop a more refined coating through use, e.g., frying or searing, and darken over time. This entire process is known as “‘seasoning.’ The color of the coating is commonly known as its ‘patina.’

The process begins by choosing an animal fat or vegetable oil to apply on the surface of the pan. There is much controversy regarding the correct oil to use. Lodge Mfg uses a proprietary soybean blend in their base coats as stated on their website. Others use lard, or animal fats. Some advocate the use of flax seed oil. There is no consensus on the issue and many have reported mixed results from the various fats. The only clear consensus with the initial process is to dry the pan through heat and layer the oil on the pan very thinly. The next part of the process is heat and duration.

Once the pan has been heated, dried, and thinly layered with oil or fat, it is placed in an oven, grill, or other heating enclosure for the oil to be polymerized onto the metal’s surface. The process of polymerization is dependent on the oil, temperature of the enclosure, and the duration. As with choosing the correct oil or fat, there is also no clear consensus with the correct temperature and duration. Some recommend high temps above 500F (260°C). Some recommend a lower temp below 300F (150°C). Some say that a temperature around the smoke point of the oil or fat should be targeted since this will allow vaporization of impurities from the oil, and polymerization and carbonization to occur.

And, there is also no clear determination of the correct duration of heat to use. Anywhere from half an hour to an hour is often recommended. Finally, this entire process needs to be repeated several times to develop the base coat, and may require a whole day to complete.

If it is not pre-seasoned, a new cast iron skillet or dutch oven typically comes from the manufacturer with a protective coating of wax or shellac, otherwise it would be rusted. This must be removed before the oven is used. An initial scouring with hot soapy water will usually remove the protective coating. Alternatively, for woks, it is common to burn off the coating over high heat (outside or under a vent hood) to expose the bare metal surface. For already-used pans that are to be re-seasoned, the cleaning process can be more complex, involving rust removal and deep cleaning (with strong soap or lye, or by burning in a campfire or self-cleaning oven) to remove existing seasoning and build-up.

A damaged pan can be reseasoned by stripping the pan down to bare metal, and re-seasoning.

As with other cast iron vessels, a seasoned pan or dutch oven should not be used to cook foods containing tomatoes, vinegar or other acidic ingredients. These foods will damage the new seasoning. Instead, newly seasoned ovens should be used to cook food high in oil or fat, such as chicken, bacon, or sausage, or used for deep frying. Subsequent cleanings are usually accomplished without the use of soap. Because modern cleaning methods (detergent soaps, dishwashers) will destroy the seasoning on cast iron, manufacturers and cookbook authors recommend only wiping the pans clean after each use, or using other cleaning methods such as a salt scrub or boiling water.

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