Food Science Basics: Heat Transfer
The Culinary Institute of America
Radiation is the transfer of energy through waves of electromagnetic energy that travel rapidly through space. Radiation does not require direct contact between the energy source and food. When the waves traveling through space strike matter and are absorbed, they cause molecules in the matter to vibrate more rapidly, increasing the temperature. Two types of radiation are important in the kitchen: infrared and microwave.
Sources of infrared radiation include the glowing coals of a charcoal grill or the glowing coils of an electric toaster, broiler, or oven. Waves of radiant energy travel in all directions from these heat sources. Foods and cookware that absorb the energy waves are heated. Dark, dull, or rough surfaces absorb radiant energy better than light-colored, smooth, or polished surfaces. Transparent glass permits the transfer of radiant energy, so conventional oven temperatures should be lowered by approximately 25°F/–4°C to offset the additional energy transfer that occurs when using glass baking dishes.
Microwave radiation, produced by microwave ovens, transfers energy through short, high-frequency waves. When these microwaves are absorbed by foods, they cause the food molecules to vibrate faster, creating heat. Microwave radiation cooks foods much faster than infrared radiation because it penetrates foods several inches deep, whereas infrared is mainly absorbed at the surface. Depending on their composition, foods react differently to microwaves. Foods with high moisture, sugar, or fat contents absorb microwaves best and heat up more readily.
Microwave cooking has a few drawbacks, however. It is best suited to cooking small batches of foods. Meats cooked in a microwave oven lose greater amounts of moisture and easily become dry. Microwave ovens also cannot brown foods, and metal cannot be used in them because it reflects the microwaves, which can cause fires and damage the oven.
Understanding how food reacts under certain conditions is essential to becoming a professional chef. From creating a flavorful dish to developing an innovative shortcut, chefs face challenges every day.
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