Part 27

=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.

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One safe rule for the cook is, that it is better to cook most foods too much than too little; overcooking is uncommon and harmless, while undercooked foods are common and difficult of digestion.

In partially cooked cereals, one does not know how much of the cooking has been done, but it is safe to cook all such foods at least as long as specified in the directions.

One reason why breakfast foods, such as rolled oats, are partially cooked, is because they keep longer.

As has been stated, the nutrients of the grain are found inside the starch-bearing and other cells, and the walls of these cells are made of crude fiber, on which the digestive juices have little effect. Unless the cell walls are broken down, the nutrients can not come under the influence of the digestive juices until the digestive organs have expended material and energy in trying to get at them. Crushing the grain in mills, and making it still finer by thorough mastication breaks many of the cell walls, and the action of the saliva and other digestive juices also disintegrates them more or less, but the heat of cooking accomplishes the object much more thoroughly. The invisible moisture in the cells expands under the action of heat, and the cell walls burst. The water added in cooking also plays an important part in softening and rupturing them. Then, too, the cellulose itself may be changed by heat to more soluble form. Heat also makes the starch in the cells at least partially soluble, especially when water is present. The solubility of the protein is probably, as a rule, somewhat lessened by cooking, especially at higher temperatures. Long, slow cooking is therefore better, as it breaks down the crude fiber and changes the starch to soluble form without materially decreasing the solubility of the protein.

“In experiments made with rolled oats at the Minnesota Experiment Station, it appeared that cooking (four hours) did not make the starch much more soluble. However, it so changed the physical structure of the grains that a given amount of digestive ferment could render much more of it soluble in a given time than when it was cooked for only half an hour.

“On the basis of the results obtained, the difficulty commonly experienced in digesting imperfectly cooked oatmeal was attributed to the large amounts of glutinous material which surrounds the starch grains and prevent their disintegration. When thoroughly cooked the protecting action of the mucilaginous protein is overcome, and the compound starch granules are sufficiently disintegrated to allow the digestive juices to act. In other words, the increased digestibility of the thoroughly cooked cereal is supposed to be largely due to a physical change in the carbohydrates, which renders them more susceptible to the action of digestive juices.”

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=Pastry.= Pastry owes its harmful character to the interference of fat as shown on page 198, with the proper solution of the starch,—at least such pastry as requires the mixing of flour with fat; the coating of these granules with fat prevents them from coming in contact with liquids; the cells cannot absorb water, swell and burst so that they may dissolve. The fat does not furnish sufficient water for this and so coats the starch granules as to prevent the absorption of water in mixing, or of the saliva in mastication. This coating of fat is not relieved until late in the process of digestion, or until the food reaches the intestines. This same objection applies to rich gravies, unless the flour be dissolved in water and heated before being mixed with the fats. The objection, therefore, is to such pastry as is made by mixing flour with fat, as in pie crust; it does not apply to most puddings.

Heat, in cooking, causes a combustion of the carbonic acid gas and the effort of this gas to escape, as well as the steam occasioned by the water in the food, causes the bubbles. When beaten eggs are used, the albuminoids in the bubbles expand the walls, which stiffen with the heat and cause the substances containing eggs to be porous.

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Since the root vegetables contain a large proportion of carbohydrates, they should be well cooked, in order that the cells may be fully dissolved, and the crude fibre broken.

Vegetables are best cooked in soft water, as lime or magnesia, the chemical ingredients which make water “hard”, make the vegetables less soluble.

Vegetables and fruits become contaminated with the eggs of numerous parasites from the fertilizers used; hence they should be thoroughly washed.

The objection to frying meats are equally strong in regard to vegetables. The coating of vegetables with the hot fat retards digestion, as shown on page 198.

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“In different countries opinions differ markedly regarding the relative wholesomeness of raw and cooked fruit. The Germans use comparatively little raw fruit and consider it far less wholesome than cooked fruit. On the other hand, in the United States raw fruit of good quality is considered extremely wholesome, and is used in very large quantities, being as much relished as cooked fruit, if indeed it is not preferred to it. It has been suggested that the European prejudice against raw fruit may be an unconscious protest against unsanitary methods of marketing or handling and the recognition of cooking as a practical method of preventing the spread of disease by fruit, accidentally soiled with fertilizers in the fields or with street dust.

“As in the case with all vegetable foods, the heat of cooking breaks down the carbohydrate walls of the cells which make up the fruit flesh, either because the moisture or other cell contents expand and rupture the walls or because the cell wall is itself softened or dissolved. Texture, appearance, and flavor of fruit are materially modified by cooking, and, if thorough, it insures sterilization, as in the case of all other foods. The change in texture often has a practical advantage, since it implies the softening of the fruit flesh so that it is more palatable and may be more readily acted upon by the digestive juices. This is obviously of more importance with the fruits like the quince, which is so hard that it is unpalatable raw, than it is with soft fruits like strawberries. When fruits are cooked without the addition of water or other material, as is often the case in baking apples, there is a loss of weight, owing to the evaporation of water, and the juice as it runs out carries some carbohydrates and other soluble constituents with it, but under ordinary household conditions this does not imply waste, as the juice which cooks out from fruits is usually eaten as well as the pulp. Cooking in water extracts so little of the nutritive material present that such removal of nutrition is of no practical importance.

“The idea is quite generally held that cooking fruit changes its acid content, acid being sometimes increased and sometimes decreased by the cooking process. Kelhofer showed that when gooseberries were cooked with sugar, the acid content was not materially changed, these results being in accord with his conclusions reached in earlier studies with other fruits. The sweeter taste of the cooked product he believed to be simply due to the fact that sugar masks the flavor of the acid.

“It is often noted that cooked fruits, such as plums, seem much sourer than the raw fruit, and it has been suggested that either the acid was increased or the sugar was decreased by the cooking process. This problem was studied by Sutherst, and, in his opinion, the increased acid flavor is due to the fact that cooked fruit (gooseberries, currants, plums, etc.) usually contains the skin, which is commonly rejected if the fruit is eaten raw. The skin is more acid than the simpler carbohydrates united to form a complex carbohydrate. In some fruits, like the apple, where the jelly-yielding material must be extracted with hot water, the pectin is apparently united with cellulose as a part of the solid pulp. As shown by the investigations of Bigelow and Gore at the Bureau of Chemistry, 40 per cent of the solid material of apple pulp may be thus extracted with hot water, and consists of two carbohydrates, one of which is closely related to gum arabic. That such carbohydrates as these should yield a jelly is not surprising when we remember that they are similar to starch in their chemical nature, and, as every one knows, starch, though insoluble in cold water, yields when cooked with hot water a large proportion of paste, which jellies on cooling.

“When fruits are used for making pies, puddings, etc., the nutritive value of the dish is, of course, increased by the addition of flour, sugar, etc., and the dish as a whole may constitute a better balanced food than the fruit alone.”