Understanding Cooking Methods: Radiation, Convection, and Conduction

Radiation occurs when energy is transferred by waves from a source to the food. The waves themselves are not actually heat energy but are changed into heat energy when they strike the food being cooked. (Light waves, radio waves, and X-rays are examples of radiation not used for cooking.)

Two kinds of radiation:

Infrared: In a broiler, an electric element or a ceramic element heated by a gas flame becomes so hot it gives off infrared radiation, which cooks the food. High-intensity infrared ovens are designed to heat food rapidly.

Microwave: radiation generated by the oven penetrates partway into the food, where it agitates the molecules of water. The friction this agitation causes creates heat, which cooks the food. Because microwave radiation affects only water molecules, a completely waterless material will not heat in a microwave oven. Plates become hot only when heat is conducted to them by hot foods. Because most microwaves penetrate no more than about 50 mm into foods, heat is transferred to the center of large pieces of food by conduction, just as in roasting.

Convection occurs when heat is spread by the movement of air, steam, or liquid (including hot fat). There are two kinds of convection: 1. Natural: Hot liquids and gases rise, while cooler ones sink. 2. Mechanical: In convection ovens and convection steamers, fans speed the circulation of heat. Heat is transferred more quickly to the food, and the food cooks faster. Stirring is a form of mechanical convection. Thick liquids cannot circulate as quickly as thin ones, so the rate of natural convection is slower. This explains, in part, why it is so easy to scorch thick soups and sauces. The heat is not carried away from the bottom of the pan quickly enough, so it stays concentrated on the bottom and scorches the food. To prevent this, stirring will redistribute this, or also using heavy pots to distribute heat through every surface.

Conduction occurs in two ways:

1. When heat moves directly from one item to something touching it—for example, from the top of the range to a soup pot placed on it, from the pot to the broth inside, and from the broth to the solid food items in it.

2. When heat moves from one part of something to an adjacent part of the same item—for example, from the exterior of a roast to the interior, or from a sauté pan to its handle.

Heat moves rapidly through copper and aluminum, more slowly in stainless steel, more slowly yet in glass and porcelain.

Pregunta escoffier menú.

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