This section is from the book "Mrs. Rorer's Diet For The Sick", by Sarah Tyson Rorer. Also available from Amazon: Mrs. Rorer's Diet For The Sick.
The first and most important point in making good soup is to use the best of materials.
To give meat soup the slightest food value, we must change the solid meat into liquid form. To do this, the fibre must be softened, the juices and blood drawn out, and the gelatin which exists in the bone, cartilage, membranes and skin, and the mineral matter, dissolved. Cold, soft water should be used. Soft water is best because it softens the fibre, which allows the juice to escape more easily. The albumin coagulates at a low temperature, which makes it necessary to cook the soup far below the boiling point.
The second point, the utensils, is also of importance. The juices of meat are acid, and if soup is made in a tin or iron kettle, it will have a peculiar, unpleasant flavor, which is sure to be detected by the sick, as their taste is always acute. Use an ordinary porcelain lined or granite kettle, with a close-fitting lid, and for straining, a granite colander or a French puree sieve. For the last straining, use two thicknesses of cheese cloth.
To prevent too great evaporation, and to keep out the odors of other cooking in the kitchen, keep the kettle covered from the beginning to the end of the cooking.
As the water reaches 2000 Fahr. you will notice a fine, fibrous net throughout the liquid; in a moment it comes to the surface. This is the albumin, drawn out by the cold water now coagulating under the influence of the heat. As it comes to the surface, it brings with it any floating particles that may be in the water, which clarifies or clears the soup. Skim this off, and reduce the heat of the water to 180o Fahr.
Rapid boiling clouds soup.
Cooking at too low a temperature spoils the flavor.
Meat soups contain a very small amount of nourishment.
A perfectly clear soup is not nutritious; it contains only the soluble mineral matter of the meat and the flavoring. The albumin you have strained out, and the fibre has not been dissolved. Beef tea, beef essence and beef soups are, however, valuable adjuncts to diet for the sick; they give flavor to other materials, and are stimulating.
Soups are divided into three classes: perfectly clear, stimulating soups, with but a trace of nourishment; clear soups that have farinaceous substances added, moderately nourishing; and nutritious soups, made from milk, meat stock and vegetables, or from milk and vegetable substances alone.
For clear beef soup and broth, a portion of the shin is to be preferred; for beef tea, beef extract, the sticking piece is first choice; the lean round or rump second. Meat for soup or beef tea should be as free from fat as possible; for broth, beef may be used alone or in combination with mutton, veal or chicken.
A true consomme, the most expensive of clear soups, should be made from veal and beef, and to give it an especial flavor for the sick, add the carcase of a roasted chicken.
Prolonged soaking in cold water will draw out the juices and flavoring quite equal to long cooking.