Pot Roasts. In the case of a pot roast, or roast in a kettle, where it is desirable to use both the fibre of the meat and the juice, or gravy, it should be put into a little cold water and raised to about 180 degrees F., where it should be kept for some hours. The juices of the meat seep out in the gravy. The extractives are simmered down and are again poured over the meat in the rich gravy.
Frying. This is the least desirable method of cooking. Food cooked by putting a little grease into a frying pan, such as fried potatoes, mush, eggs, french toast, and griddle cakes, are more difficult of digestion than foods cooked by any other means, particularly where the fat is allowed to smoke. The fat is superheated; if a lighted match is placed near the smoke it will catch fire, showing that it is volatilizing, or being reduced to a vapor.
The extreme heat liberates fatty acids. This acrid fat soaks into the food and renders it difficult of digestion. It is wise not to employ this method of cooking.
The objection to frying does not hold so strongly in the case of vegetables, such as potatoes, if fried slowly in fat, that is not over heated, or to griddle cakes cooked slowly without smoke, or to foods immersed in grease (such as saratoga chips, doughnuts, french fried potatoes, etc.), as the large amount of fat does not permit it to get so heated. It does apply, however, if the fat is sufficiently heated to smoke.
The coating of vegetables and cereals with the hot fat prevents the necessary action of saliva upon the starch globules. As previously stated, most of the starches are digested in the mouth and the stomach, while the fats are not emulsified until they reach the intestines.
The starch globules in cereals and vegetables are in the form of cells, the covering of these cells being composed largely of nitrogenous matter. The protein is not acted upon by the saliva, and the nitrogenous matter is largely digested in the stomach. It is more easily dissolved if it is broken or softened by cooking, so that the carbohydrates can come in contact with the saliva, but if encased in fried fat, the gastric juices cannot digest the protein covering and the saliva cannot reach the starch until the fat is emulsified in the intestines. This means that wherever starch globules are surrounded with fat, the digestive ferments reach these globules with difficulty and fried foods must be digested mostly in the intestines.
Fats are readily absorbed in their natural condition, but when subject to extreme heat, as in frying, they are irritants. For this reason, eggs, poached, boiled or baked are more easily digested than fried.
Boiling, broiling and roasting are preferable to foods cooked in fats.