A. Class Experiments. Fats.
2. Find the temperatures at which butter, lard, and Crisco melt. Place two tablespoons of each fat in small beakers, stand in warm water, insert a thermometer, and note the temperature at which the fat melts.
3. Put drops of olive oil and oil of peppermint on a piece of paper and warm them. How do they differ?
4. To determine the "cracking" or "burning point" of fats: a. Test butter with blue litmus paper; then place about two teaspoons of butter in a small evaporating dish and heat until the first appearance of smoke. Determine the temperature of the fat. Hold a piece of moist litmus paper in the fumes.
b. Repeat with lard, olive oil, and Crisco. In which fats would it be best to fry?
5. Heat fat, lard, or Crisco to 355° F., and then determine in how many seconds a small piece of bread will brown in the fat. Repeat with the fat at 365° F., and at 385° F. What is the effect on the bread at the low temperature? Of the last two temperatures, which would be better for frying uncooked material like fritters? Material already cooked, such as croquettes?
B. Make Doughnuts.
Use one-eighth of the following recipe :
1 c. milk
2 tbsp. butter 1 c. sugar
4 tsp. baking powder
2 tsp. salt
4 c. flour
1 tsp. cinnamon
1/4 tsp. nutmeg
C. Clarify the Fat Used.
Heat the fat slowly with a few slices of raw potatoes; then strain through cheesecloth placed in a strainer.
Fat, a term which is used to include edible oils as well, is, like carbohydrate, a source of energy in the body. Weight for weight, fats furnish the body with two and a quarter times as much energy as do the carbohydrates.
Composition of Foods Containing much Fat.
But not all substances which are ordinarily spoken of as fats are really pure fat. Olive oil and lard are practically pure fat, but butter contains only eighty-four per cent of it, the rest being mostly water, curd, and mineral matter.
Fats are usually divided into two classes, - volatile and non-volatile fats. These terms are somewhat misleading, as the volatility does not refer to the fats themselves, but to the fatty acids which enter into their composition. Most fats are chemical compounds of glycerine and fatty acids. Those that are made from volatile fatty acids have low melting points and are more digestible than most of the fats of the other class. They are found in milk fat, hence also in cream and butter.
The non-volatile fats of food are chiefly three: olein, palmitin, and stearin. The first of these has so low a melting point that it is an oil at ordinary temperatures. Olive and cottonseed oils are largely composed of olein. Stearin has the highest melting point of the three, and so fats like suet, which is largely stearin, are fairly firm. The melting point of palmitin is between that of the other two. Most of the fat of foods is a mixture of these nonvolatile fats. The melting point of some of them is shown in the following table:
Stearin ....................... Mutton fat .............. Palmitin..................... Beef fat ................... Bacon fat..................
Fats which have a melting point of 110° or below, seem to be digested about equally well. However, the eating of fat causes the food to remain longer in the stomach and so retards the processes of digestion. In some cases this may cause digestive disturbances by allowing more time for the decomposition of food in the digestive tract through the action of bacteria, but fat itself is not liable to objection-able decomposition during digestion. Fat which has been heated to too high a temperature is much more liable to cause digestive difficulties, because, apparently, of the presence of irritating decomposition products. Hence it is necessary in selecting a fat for frying to consider the temperatures at which this decomposition takes place. The following is a table of "cracking points", as the decomposition temperatures are often called:
Olive oil..................... Cottolene....................
Fats vary greatly in cost, olive oil being expensive. Advantage should be taken of the lower price asked for it in quantity. (Buying oil in a small bottle is very extravagant.) Italian oil in bulk is usually cheaper than French oil. Good American oil is manufactured in California.
Butter and cream are also expensive sources of fat, but they are very desirable for children and invalids on account of their ease of digestion. Bacon fat ranks with butter and cream both in digestibility and expense. Fat left from the frying of bacon should be carefully saved for sauteing, as should that tried out from the fat of beef, veal, pork, and chicken. Even the fat which hardens on soup stock can be used. Gravies, sauces, cream soups, and gingerbread may all be made with such fat, and vegetables and meat may be sauted in them. Mutton fat1 has so strong a flavor that it is usually objected to on this account.
1 For ways of utilizing this fat, see U. S. Dept. of Agriculture, Bulletin No. 310, page 11.
Yolks of eggs are one-third fat and furnish fat in a very digestible form.
U. S. Dept. of Agriculture. Bulletin No. 310. "Digestibility of Some Animal Fats."
1. How are these fats obtained: butter, lard, cottonseed oil, olive oil, beef fat, lard, Crisco?
2. What does each cost per pound? Are fats sufficiently expensive foods to make it worth while to consider economy in their use?
3. Suggest good opportunities for the substitution of a cheaper fat for a more expensive one. For example, would it be better to use lard in gingersnaps or sugar cookies?
4. Discuss the digestibility of fats.
5. What care must be taken in frying food to make it as digestible as possible?
6. Why is fat-soaked food indigestible?
7. What is the difference between sauteing and frying?
8. Why does the cooking of slices of raw potato in fat clarify it?
9. Why is deep-fat frying dangerous, especially over an open flame?
10. Why should fried foods be drained on unglazed paper?
11. Why should foods to be fried be as dry as possible?
12. How is soap manufactured?