Seasoning is the process of treating the surface of a metal saucepan, wok

Wok

A wok is a versatile round-bottomed cooking vessel originating in China. It is used especially in East and Southeast Asia.Woks are most often used for stir frying, but can also be used in other Chinese cooking techniques, such as in steaming, deep frying, braising, stewing, smoking, or making soup...

, cast-iron cookware or other cooking vessel to create a stick-resistant coating. The seasoning procedure creates the non-stick surface from polymerized fat and oil on the surface.

Seasoning is desirable on cast-iron cookware and carbon steel cookware, because they are very porous, and otherwise they are very sticky to foods, which without a seasoned surface would cause bacteria to grow and make the cookware rust

Corrosion

Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

-prone. It is generally not desired on other types of cookware either for cosmetic reasons or because the chemical composition of the pan already results in a non-stick surface.

Unglazed stoneware

Stoneware

Stoneware is a vitreous or semi-vitreous ceramic ware with a fine texture. Stoneware is made from clay that is then fired in a kiln, whether by an artisan to make homeware, or in an industrial kiln for mass-produced or specialty products...

 bakeware is non-porous and therefore does not require seasoning before use. However, it may be oiled or greased before use to produce a more non-stick surface for convenience, to make food removal easier.

Metal surface chemistry

The seasoned surface consists of a polymerized

Polymerization

In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...

 and plasticized

Thermoplastic

Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...

 coating.

The process of heating cookware causes the oil to oxidize is analogous to the hardening of drying oil

Drying oil

A drying oil is an oil that hardens to a tough, solid film after a period of exposure to air. The oil hardens through a chemical reaction in which the components crosslink by the action of oxygen . Drying oils are a key component of oil paint and some varnishes...

 used in oil paints, or to varnish a painting. But whereas the curing

Curing (chemistry)

Curing is a term in polymer chemistry and process engineering that refers to the toughening or hardening of a polymer material by cross-linking of polymer chains, brought about by chemical additives, ultraviolet radiation, electron beam or heat...

 of oils is the result of autoxidation

Autoxidation

Autoxidation is any oxidation that occurs in open air or in presence of oxygen and/or UV radiation and forms peroxides and hydroperoxides. A classic example of autoxidation is that of simple ethers like diethyl ether, whose peroxides can be dangerously explosive. It can be considered to be a slow,...

 at room temperature for a painting, for a pan, the thermoxidized oil undergoes a conversion into the hard surface of the seasoned pan at the high temperatures of cooking.

When oils or fats are heated in a pan, multiple degradation reactions occur, including: autoxidation

Autoxidation

Autoxidation is any oxidation that occurs in open air or in presence of oxygen and/or UV radiation and forms peroxides and hydroperoxides. A classic example of autoxidation is that of simple ethers like diethyl ether, whose peroxides can be dangerously explosive. It can be considered to be a slow,...

, thermal oxidation

Thermal oxidation

In microfabrication, thermal oxidation is a way to produce a thin layer of oxide on the surface of a wafer. The technique forces an oxidizing agent to diffuse into the wafer at high temperature and react with it. The rate of oxide growth is often predicted by the Deal-Grove model...

, polymerization

Polymerization

In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...

, 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

Oven

An oven is a thermally insulated chamber used for the heating, baking or drying of a substance. It is most commonly used for cooking. Kilns, and furnaces are special-purpose ovens...

 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

Rust

Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...

 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

Hydrophobic effect

The hydrophobic effect is the observed tendency of nonpolar substances to aggregate in aqueous solution and exclude water molecules. The name, literally meaning "water-fearing," describes the segregation and apparent repulsion between water and nonpolar substances...

, 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).

Mexican clay pots

Mexican clay pots of the type used over a direct flame are seasoned without the use of cooking oil or fat. To season a Mexican clay pot, fill the pot with water and heat the pot over a direct flame, or on a stovetop using a heat diffuser. Allow the water to boil for a few minutes, then discard the water. Only lead-free clay pots should be used for cooking.

Clay bakeware can be soaked in water before each cooking use, since the water absorbed will be released during the cooking process and maintains moisture in the food.

Cast-iron or metal cookware

A new pan (bare metal) is porous and will grab food tightly, and must either be oiled before cooking or seasoned. 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 colour of the coating is commonly known as its "patina".

To season a pan (e.g., to season a new pan, or to replace damaged seasoning on an old pan), the following is a typical process: (a) cleaning the cookware to expose the bare metal, (b) applying a layer of animal fat

Animal fat

Animal fats are rendered tissue fats that can be obtained from a variety of animals.- Pet nutrition :In pet nutrition, the source of animal fat concerns food manufacturers. AAFCO states that animal fat is "obtained from the tissues of mammals and/or poultry in the commercial processes of rendering...

 or vegetable oil, and (c) heating the cookware to generate the seasoned coating. If it is not pre-seasoned, a new cast iron skillet or dutch oven

Dutch oven

A Dutch oven is a thick-walled cooking pot with a tight-fitting lid. Dutch ovens have been used as cooking vessels for hundreds of years....

 typically comes from the manufacturer with a protective coating of wax or shellac

Shellac

Shellac is a resin secreted by the female lac bug, on trees in the forests of India and Thailand. It is processed and sold as dry flakes , which are dissolved in ethyl alcohol to make liquid shellac, which is used as a brush-on colorant, food glaze and wood finish...

, 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 wok

Wok

A wok is a versatile round-bottomed cooking vessel originating in China. It is used especially in East and Southeast Asia.Woks are most often used for stir frying, but can also be used in other Chinese cooking techniques, such as in steaming, deep frying, braising, stewing, smoking, or making soup...

s, 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.

The procedure for seasoning a cast iron pan is described as follows :

• Wash the cookware with hot, soapy water and a stiff brush. (Soap can be used this time because the surface has not yet been seasoned).
• Rinse and dry completely.
• Apply a thin, even coating of melted solid vegetable shortening or cooking oil to the cookware (inside and out).
• Place aluminum foil on the bottom rack of the oven to catch any dripping.
• Set oven temperature to 400 °F (204 °C).
• Place cookware upside down on the top rack of the oven.
• Bake the cookware for at least one hour. After the hour, turn the oven off and let the cookware cool in the oven.
• Store the cookware uncovered, in a dry place when cooled.

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. The precise details of the seasoning process differ from one source to another, and there is much controversy regarding the correct oil to use. There is also no clear consensus with the correct temperature and duration. Lodge Manufacturing 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. Likewise, the recommended temperature for seasoning varies to high temperatures above 500 °F (260 °C), while some recommend a lower temp below 300 °F (149 °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.

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

Care

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

Deep frying

Deep frying is a cooking method in which food is submerged in hot oil or fat. This is normally performed with a deep fryer or chip pan; industrially, a pressure fryer or vacuum fryer may be used....

. 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.

Other surface types

There are other surfaces on cookware which are stick-resistant. See also Non-stick pan

Non-stick pan

Non-stick pans are cooking pans made from or coated with materials designed to prevent food from sticking to their surface during the cooking process. Most non-stick pans are made using Teflon coating although newer materials are also used...

s.

In the process of bluing

Bluing (steel)

Bluing is a passivation process in which steel is partially protected against rust, and is named after the blue-black appearance of the resulting protective finish. True gun bluing is an electrochemical conversion coating resulting from an oxidizing chemical reaction with iron on the surface...

, there is formed an oxidizing chemical reaction with iron on the surface selectively forming magnetite

Magnetite

Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...

 (Fe₃O₄), the black oxide of iron (as opposed to rust

Rust

Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...

, the red oxide of iron (Fe₂O₃)). Black oxide provides minimal protection against corrosion, however, unless also treated with a water-displacing oil to reduce wetting and galvanic action.

External links

• Chemistry of Cast Iron Seasoning: A Science-Based How-To
• How to season bare cast iron cookware from Lodge
• Seasoning cast iron from the Kitchen Emporium
• HOW TO SEASON A NEW BLACK POT from Chef John Folse
• THE SCOOP ON SEASONING, CLEANING AND RESTORING CAST IRON from Melinda Lee
• Cast Iron Cooking, from Holiday Cook
• How do you season cast iron? from Jace's Cast Iron Corner