The greatest care must be observed to keep the scraps perfectly sweet and fresh until needed, as stale meat is exceedingly unwholesome.  If the scraps are mostly cooked meats and bones, a small portion of raw, lean meat should be used with them; it need not be of the choicest quality; tough, coarse meat, when fresh and good, can be advantageously used for soup stock.

If fresh material is to be procured, select for beef soups a piece from the shin or lower round; the same choice of pieces may be made of veal; of mutton, pieces from the forequarter and neck are best.

In preparing meat for soup, if it is soiled, scrub the outside thoroughly with a clean cloth wet in cold water, or cut away the soiled portion.  Break the bones into as small pieces as convenient; cut the meat into inch dice, remove the marrow from the bones, and put it aside.  If added to the stock, it will make it greasy.

Having selected proper material and prepared it for use, the next step is to extract the juices.  To do this put it into cold water, bring very gradually to the boiling point,—­an hour is not too long for this,—­then cook slowly but continuously.  In the observation of these simple measures lies the secret of success in stock-making.

The albuminous elements of the meat, which are similar in character to the white of an egg, are readily dissolved in cold or tepid water, but boiling water coagulates them.  If the meat is put into boiling water, the albumen coagulates, or hardens, forming a sort of crust on the outside of the meat, which prevents the inner juices from escaping; on the contrary, if the meat is put to cook in cold water, and is gradually raised to the boiling point, the soaking and simmering will easily extract and dissolve the juices.

Salt likewise hinders the extraction of the meat juices, and should not be added to stock during its preparation.

The best utensil for use in the preparation of stock is a soup digester.  This is a porcelain-lined kettle, resting on standards, with a cover fitting closely into a groove, so that no steam can escape except through a valve in the top of the cover.  In this the meat can be placed and allowed to cook for hours without burning.  An ordinary granite-ware kettle with tightly fitting cover set on a stove ring or brick, answers quite well.  It should, however, be kept entirely for this purpose.  A double boiler is also suitable.

The correct proportion of water is to be used is about one quart to each pound of meat and bones, though this will vary somewhat with the material and the length of time required for cooking.  The scum which is thrown to the surface of the water during the cooking process is composed of blood and other impurities, and should be removed as rapidly as it rises.  If allowed to remain after the water reaches the boiling point, it will become incorporated into the stock and injure it in flavor and wholesomeness.