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4 Cards in this Set
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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.) Two kinds of radiation are used in the kitchen: 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 (p. 112) 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. |
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Conduction 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. Different materials conduct heat at different speeds. Heat moves rapidly through copper and aluminum, more slowly in stainless steel, more slowly yet in glass and porcelain. Air is a poor con- ductor of heat. |
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Convection |
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. Thus, in any oven, kettle of liquid, or deep-fat fryer a constant, natural circulation distributes heat. 2. Mechanical. In convection ovens and convection steamers, fans speed the circulation of heat. Thus, 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. Stirring redistributes the heat and helps pre- vent this. (Using heavy pots made of a material that conducts heat well also helps prevent scorching because the pot conducts the heat more quickly and evenly across the bottom and up the sides.onvection is the process that carries the heat from the heat source to the food. Once the carrier of the heat (air or liquid) comes in contact with the food, the heat is transferred from the carrier to the food by conduction. |
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We say a food is “done” when two things have happened: |
1. The interior temperature has risen to the desired degree. Interior temperature is the most important factor when we are cooking tender meats. The difference between rare, medium, and well done (p. 481) is a difference in temperature, and we can measure this doneness with a thermometer. Interior temperature is also important for food safety, 2. The desired changes have taken place in the food. |
