Radiation

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.)

1. Infrared.

   Broiling is the most familiar example of infrared cooking. 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.

2. Microwave.

   In microwave cooking, the radiation generated by the oven penetrates partway into the food, where it agitates the molecules of water. Recall from our earlier discussion that heat is the motion of molecules. Thus, as the molecules move faster, the temperature of the food rises and the food is cooked.

   • 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 2 inches (50 mm) into foods, heat is transferred to the center of large pieces of food by conduction, just as in roasting.

   Cooking with microwaves is discussed in more detail later in this chapter.