This section is from the book "Economical Cookery", by Marion Harris Neil. Also available from Amazon: Economical Cookery (1918).
The principle underlying the making of soups, as in the case of stock, is extraction. Soups depend for their success on the flavors and goodness extracted from the materials used in their manufacture, and this is especially the case when water has to be used instead of good stock. The value of soup is chiefly as a stimulator of appetite, except in cases where the food value has been increased, as in lentil soup. A well-flavored soup, made from stock containing " extractives " and gelatine from bones and meat respectively, especially if it is served hot, has the effect of inducing an increased flow of the gastric juices, and therefore it aids in the digestion of the meal that follows. For this reason soups are served at the beginning of a meal, and are essentially stimulative rather than satisfiers of appetite.
The aims in soup-making are:
1. To produce a well-flavored soup.
2. To keep the soup a good color.
3. To make it clear, or of the right consistency, according to the character of the soup.
4. To keep it free from grease.
The rules for making soup vary with the character of the soup to be made, and before dealing with these rules, it is necessary to know something of the various classes of soup. These, though so numerous, can, roughly speaking, be divided into two great classes, clear and thick.
Clear. Under the heading of clear soups are included consomme's, or "cleared" soups, broths, and bouillons.
Thick. This class includes thick soups, purees, bisques, cream soups, cosmopolitan, and fruit soups.
Consommes are made from carefully prepared first stock, cleared with lean beef and the whites and shells of eggs; a characteristic flavoring or garnish is added at the end to give the soup its distinguishing name, such as Consomme Julienne (with shreds of vegetables).
Broths are made from first stock, seasoned to taste, and with the addition of pearl barley or rice, and vegetables. They may be prepared from lean mutton, beef, chicken, rabbit, or veal.
Bouillon is a broth made from beef. It is simply unclarified stock, to which are added various grains such as rice, barley, sago, etc., and vegetables either cooked in the broth or separately, and served in small pieces. This depends for its food value principally on the stock, which must be strong and well flavored. Frequently there is served as another course the meat from which the broth has been prepared.
Thick Soup is stock which is thickened by some foreign substance such as cornstarch, arrowroot, bread, cereals, eggs, etc. This stock must be of good quality, for the thickening substance cannot be used in sufficient quantity to increase perceptibly the food value.
Purees are thick soups, but the thickening is due to the substance of which the puree is composed, which is sieved and incorporated with the soup. A certain amount of starch, such as flour or cornstarch, or other binding material, is needed, not to thicken but to bind the liquid and solid parts of the soup together and prevent the heavy substance from separating or settling at the bottom. Frequently the material of which the puree is composed is of such a nature as not to require the addition of meat, such as lentils, beans, peas, etc.; others are improved by being made of second stock, while others require as good stock as can be made, there being little or no nutriment in the substance itself.
Bisques are cream soups made with shellfish, such as oysters, lobsters, shrimps, prawns, clams, etc. They are made as for cream soups, and some small pieces of the fish used in making are added as a garnish.
Cream Soups partake of the nature of purees, but their distinguishing feature is that the binding agent is cream and yolks of eggs, instead of flour or cornstarch.
The same rules as for purees apply until after sieving, and then the cream and yolks of eggs must be added carefully, and the soup must on no account be allowed to boil during reheating, or the albumen in the eggs will harden or coagulate, causing curdling.
Cosmopolitan Soups are soups which are peculiar to different countries, such as Scotch Broth, Olla Podrida, and Pot-au-feu. They are made according to the rules for the kind of soup upon which they are based.
Fruit Soups are specially recommended for use in summer, when they will be found refreshing and cooling. They can be made with either fresh or dried fruit, and the method for all is very similar. The fruit is stewed until soft and reduced to a pulp with water and sugar, and then strained or sieved. A little spice, such as nutmeg, ginger, or cinnamon, or the grated rind of a lemon or orange, is generally added to give flavor. Some fruit soups require a little thickening to be added. Red or white wine may also be used for flavoring. These soups are served either hot or cold with rusks, zwieback, toast, crackers, puffed rice or wheat, etc., according to fancy.