The various ways in which cooking affects vegetables should be thoroughly understood by the housewife. In the first place, some methods conserve the food material whereas others waste it.
For instance, boiling in water, which is probably one of the most common ways of cooking vegetables, is decidedly advantageous in some respects, but the water dissolves much of the soluble material, such as mineral salts, sugar, etc., found in the vegetables, so that unless some use is made of this water in the cooking of other foods, considerable waste results.
On the other hand, steaming and baking permit no loss of food material, and so they should be applied to vegetables whenever it is desired to conserve food substances.
The flavors of vegetables are greatly changed during the process of cooking, being increased in some cases and decreased in others. In the case of such strongly flavored vegetables as cabbage, cauliflower, onions, etc., it is advisable to dissipate part of the flavor.
Therefore such vegetables should be cooked in an open vessel in order that the flavor may be decreased by evaporation. Vegetables mild in flavor, however, are improved by being cooked in a closed vessel, for all their flavor should be retained.
The overcooking of vegetables is sometimes responsible for an increase of a disagreeable flavor. Another feature of vegetables often changed by cooking is their color. For instance, green vegetables do not, upon cooking, always remain green. In many cases, the color may be improved by adding a very small quantity of soda to the water in which the vegetables are cooked.
Attention should also be given to the length of time vegetables are subjected to heat, for the over boiling of some vegetables is liable to develop an unattractive color in them.
This is particularly the case with cabbage, cauliflower, and Brussels sprouts, which develop not only a strong, disagreeable flavor but also a reddish color when cooked too long.
The application of heat to vegetables also has a definite effect on them. By sufficient cooking, the cellulose of vegetables is softened to the extent that it is less irritating and much more likely to be partly digested than that of raw vegetables. The acids of fruits increase upon cooking, and so the acidity of vegetables is increased to a certain extent.
Vegetables that contain starch are rendered digestible in no other way than by cooking. On the other hand, the protein material of this food is coagulated by the application of heat, just as the white of an egg or the tissue of meat is coagulated and hardened. However, cooking is the only means of softening the cellulose that surrounds this material.
Still, high-protein foods, such as beans, peas, and lentils, can be much improved if they are cooked in water that is not very hard. The lime in hard water has a tendency to harden them to the extent that they require a much longer time to cook than when soft water is used.
These vegetables may be still further softened by the addition of a small quantity of soda to the water in which they are cooked, but care should be taken not to use too much soda, as it will injure the flavor.
When soda is used, the vegetable should be parboiled for 10 or 15 minutes in the soda water and then drained and cooked in fresh water. This method, of course, does not apply to vegetables that are cooked in soda water to retain their color.
Salt is always added in the cooking of vegetables to season them. In the use of salt, two important points must be borne in mind: first, that it has the effect of hardening the tissues of the vegetable in much the same manner as it hardens the tissues of meat; and, secondly, that it helps to draw out the flavor of the vegetables.
These two facts determine largely the time for adding the salt. If an old, tough, winter vegetable is to be prepared, it should be cooked until nearly soft in water that contains no salt, and the salt should be added just before the cooking is finished.
When it is desired to draw out the flavor, as, for instance, when vegetables are cooked for soup or stews, the salt should be supplied when the vegetables are put on to cook.
Young tender vegetables may be cooked in salt water, but as such water extracts a certain amount of flavor, an effort should be made to use it in the preparation of stews, sauces, and soups.