FOOD COMPONENTS 

In order for food to be cooked, heat must be transferred from the heat source (such as a gas flame or heating element coil) to and through the food. Understanding the way in which heat is transferred and the speed at which it is transferred helps to control the cooking process. Heat could be transferred by Conduction, Convection or Radiation.

Occurs in two ways:

1. When heat moves directly from one item to something touching it.

2. When heat moves from one part of something to an adjacent part of the same item. Different materials conduct heat at different speeds. Heat moves rapidly through copper and aluminum, more slowly through stainless steel and slower yet in glass and porcelain. Air is a very poor conductor of heat.

Convection occurs when the movement of air, steam or liquid (including hot fat) spreads heats. There are two types of convection:

1. Natural. Hot liquids and gases rise, while cooler ones sink. Thus, in any oven, a kettle of water or deep fat fryer there is a constant natural circulation that distributes the heat.

2. Mechanical. In convection ovens and steamers, fans speed the circulation of heat. Thus, the heat is circulated much faster and more evenly and thus the food cooks faster. Stirring is a mechanical form of convection. Thick liquids cannot circulate as quickly as thin ones, so the rate of natural circulation is slower.

Occurs when energy is transferred by waves from the source to the food. The waves themselves are not actually heated energy but are changed into heat energy when they strike the food being cooked. There are two types of radiation used in the kitchen:

Broiling is the most familiar example in 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. There are also high-intensity infrared ovens, designed to heat food rapidly.

In microwave cooking, the radiation generated by the oven penetrates partway into the food, where it agitates the molecules of water. The friction caused by this agitation creates intense heat, which cooks the food. Because microwave radiation affects only water molecules, a completely waterless material will not heat up in the microwave.

Plates become hot only because of the conduction of heat from the food. Also, because microwaves penetrate no more than 2” into the foods, heat is transferred to the center of large pieces by conduction.