LESSON XXXVI
FAT AS A FRYING MEDIUM—DIGESTION OF FAT
EXPERIMENT 36: ACTION OF OIL AND WATER.—Pour a little corn or cottonseed oil into a test tube, add the same quantity of water, and shake the tube. Set the tube aside for a minute and examine. Which material rises to the top? Is oil soluble in water? What application can be made from this concerning the effectiveness of cleaning the fat of meats with water?
EXPERIMENT 36: EMULSION OF FAT.—In a test tube put a bit of soap and 2 tablespoonfuls of water. Heat until the soap is melted. Add 1/2 teaspoonful of vegetable oil. Shake the mixture and then examine. What familiar food does the mixture look like? Set the tube aside for a minute. Does the oil rise to the top as in Experiment 35? The fat is in an emulsified condition.
BREAKING UP OF FATS.—Fats and oils are not soluble in any substance found in the digestive juices, but they are acted upon by an enzyme [Footnote 41: Steapsin or lipase is the enzyme found in the pancreatic juice which acts upon fat.] and by an alkaline substance found in the pancreatic juice. The enzyme breaks up some of the fat into a fatty acid [Footnote 42: Fatty acids are substances related to fats; they have certain acid properties.] and glycerin.
During digestion, fat is emulsified, i.e. divided into tiny globules which do not coalesce.
When a fat is emulsified, it often looks like milk. (Milk contains fat in an emulsified form; the fat separates, however, by standing and rises to the top to form cream.) Fats can be emulsified by several different substances. A soap solution is one of the substances that will emulsify fats. (The action of soap solution in emulsifying fat was shown in Experiment 36.)
If fats are emulsified by means of soap, one might ask where the soap comes from in the process of digestion. The soap is thought to be formed by the action of the alkali of the pancreatic juice upon some of the fatty acids formed by the splitting up of the fat. By means of the soap thus formed, fat is emulsified during digestion. During digestion, fat is broken up into fatty acids and glycerin.
FRYING AND DIGESTION.—Fat is a slowly digesting foodstuff. Not only fats, but foods coated with fat are digested slowly. Because of the longer time in the digestive tract, foods may cause digestive disturbances.
When fats are heated to a high temperature, they are decomposed and irritating substances (free fatty acids) are formed. These substances are absorbed by foods which are browned in fats.
It is well, then, to have the least possible quantity of fat soak into foods cooked in fats. It has been found that foods soak up much more fat when sauted (i.e. browning in a small quantity of fat) than when fried. The greatest care should be taken in frying, however, to have the fat and the food to be fried in such condition that as little fat as possible will be absorbed. The fat should be sufficiently hot (see Experiments 32 and 33), the food as dry as possible, and the browned food drained on paper.
Care should be taken not only in frying foods, but in avoiding the use of an excessive amount of fat such as butter, cream, and vegetable oils in sauces, dressings, and pastry.
CROQUETTES.—Croquettes are cooked vegetable, cereal, meat, or fish mixtures dipped in dried crumbs and eggs and browned in deep fat. These food mixtures are shaped in various ways. Rice and potato croquettes are usually cylindrical in shape, while chicken croquettes are formed into cones.
Croquettes may be dipped in melted butter or substitute or they may be "dotted" with bits of fat and browned in the oven or broiling oven instead of frying in deep fat.
Starch occurs in considerable quantity in the vegetables and cereals commonly used for croquettes. Meat and fish are usually mixed with a thick White Sauce when used for croquettes, hence croquettes invariably contain a starchy substance. If croquette ingredients are heated while mixing, it is necessary to cool them thoroughly before shaping, in order that the starch may be as stiff as possible.
POTATO CROQUETTES
1 pint mashed potatoes Celery salt 2 tablespoonfuls butter Onion juice Cayenne 1 teaspoonful chopped parsley 1 teaspoonful salt 1 egg-yolk or 1/2 egg
Mix ingredients together, shape into smooth round balls and then into cylinders. Roll in dried bread crumbs, eggs, and crumbs again (see Fried Oysters). Fry in deep fat until brown.