How do we know to when foods are done? Tests for doneness are not precise; however, most of them work reasonably well.
One method to test for doneness is to use a thermometer. It can be especially useful when roasting meats.
There are other tests which are more subjective. Examples of these include judging the doneness
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of stirred custard by the way it coats a spoon
of a soft pie filling by its thickness
of a poached or fried egg by the opaqueness of the white
of baked product like cake by its springiness when touched by a finger
of fruits, vegetables, and meats by the ease with which they are pierced by a fork.
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Browness of a baked product. A loaf of bread, for example, usually gets brown some time before the center of the loaf gets hot enough to set the crumb. Time tables are useful guides to approximate cooking times.
Why is heating important? What does it do in foods?
The heating of foods effects their nutritional value. In general, the destruction of nutrients is minimized by shortening cooking time and decreasing temperature. When a given thermal input is required, however, as in thermal processing, the minimum overall nutritional deterioration is generally attained by using high temperatures for a short time.
Various potentially pathogenic food-borne microorganisms can multiply, under the proper conditions: temperatures within the range of 45 F(7-2C) to 140 (60C). Bacterial generation time can be as short as 20 to 30 minutes.
COOLING FOODS
Discussion to this point has centered on heating foods. In many instances, however, a food needs to be cooled instead. The rate of cooling of a food depends in part upon the food container and the cooling environment. When hot food is cooled in air, the ability of the material to conduct heat is not a primary consideration because air is a poor conductor of heat. Foods will cool more rapidly in air if they are in a cibtauber which permits the passage of radiant energy. A pan made of glass or enameled iron transmits radiant energy from hot food to cooler air more rapidly than those of other materials, just as it transmits radiant energy more rapidly to the food. If the container of food is placed in water to cool, the ability of the material to conduct heat is of primary consideration and for this metals are superior. Stirring the water surrounding the metal container speeds the cooling. A mixing bowl made of pottery, which is not a good conductor, is a poor choice of container if rapid cooling is desired.
The use of energy for refrigeration in homes has increased in recent years. At the same time that larger refrigerators are replacing smaller ones, the efficiency of energy use has somewhat decreased with the development of such convenience features as frostfree refrigerators and automatic ice makers.
