In the body, these foods, like carbohydrates, give energy; in fact weight for weight they furnish more than twice as much energy as carbohydrates. There is, for example, about as much fat by weight in one pound of butter as there are carbohydrates in one pound of tapioca. By measurement it has been found that one pound of butter gives to the body almost two and one fourth times as much energy as does one pound of tapioca.
Fats and oils are not only used as food (butter for example) and as constituents of foods (fat in pastry), but as a medium for cooking. The use of fat as a cooking medium follows:
EXPERIMENT 31: TEMPERATURE AT WHICH FATS AND OILS DECOMPOSE OR "BURN."-- Into each of 6 test tubes put 2 teaspoonfuls of butter, cottonseed oil, corn oil, beef drippings, lard, and Crisco. Gently heat each one of the fats or oils until fumes first arise from them. Then insert a thermometer [Footnote 39: Care should be taken in using a thermometer in hot fat. It should be allowed to cool before washing.] in each tube and note the temperatures. These are the temperatures at which the various fats decompose. Record these temperatures in your notebook.
How do the decomposing temperatures of fat compare with that of boiling water? Which would be the hotter medium for cooking--hot fat or boiling water?
Which fat reaches the highest temperature before it begins to decompose? If fat is used as a medium of cooking, which of these fats, as far as temperature is concerned, would be the most desirable? Give a reason for your answer.
What is the price per pound or pint of each of these fats or oils?
Which of these are vegetable and which are animal fats or oils?
FATS FOR DEEP-FAT FRYING.--As shown by the above experiment, fat reaches a high temperature when heated. For this reason fat may be used as a cooking medium. The process of cooking food in deep fat is called frying. From the standpoint of temperature the best fat for frying is that which can be heated to a very high temperature without burning.
Other factors such as flavor and cost, however, have to be taken into consideration. Fat not only heats foods, but it imparts flavor since some of the fat in which a food is cooked, clings to the food. The costs of the various fats differ greatly. This must be regarded in selecting fats for cooking. Taking these factors into consideration, many prefer the cheaper vegetable fats for frying, while others find a mixture of beef drippings and lard satisfactory.
EXPERIMENT 32: BREAD FRIED IN "COOL" FAT (CLASS EXPERIMENT).--Put some suitable fat for frying in an iron pan and heat. Note carefully the change that takes place in fat as it heats. When the fat "foams" or bubbles, or reaches a temperature of about 300 degrees F., drop into it a piece of bread. After one minute remove the bread from the fat; examine the bread by breaking it apart to see if the fat has soaked into the bread. Is it desirable to have the fat soak into fried foods? What conclusion can you draw as to frying foods in "cool" fats?
EXPERIMENT 33: THE TEMPERATURE OF FAT FOR FRYING (CLASS EXPERIMENT).-- Continue to heat the fat of Experiment 32. When fumes begin to rise from the fat, or the fat reaches a temperature of 365 degrees F., again drop a bit of bread into it. After one minute remove the bread and examine it as above. Has as much fat soaked into it as in the first bit of bread? What conclusion can you draw from this in regard to the proper temperature for frying foods?
Cooked foods and foods needing but little cooking require a higher temperature than batters or other uncooked foods. If a bit of bread is browned in 40 seconds, the fat is of proper temperature for cooked foods and for oysters. If bread is browned in 60 seconds, the fat is of proper temperature for uncooked foods.
GENERAL RULES FOR FRYING.--Since fat, when heated, reaches such a high temperature, the kettle in which it is heated should be of iron.
If there is any moisture on foods, it must be evaporated before the foods brown.