This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
Stewing differs from boiling in the fact that the juices of the meat or vegetables are dissolved in the heated water, whereas in boiling, the juices are kept from passing out into the water by the coagulation of the external surface of the food mass produced by immersing it suddenly into boiling water. The proper temperature for stewing is between 1350 and 1600 F. In thick stews the juices dissolved in the water are eaten together with the cooked food, but in some instances, as in the making of beef tea and some kinds of soups, the aqueous solution only is used. Obviously, the more the food is subdivided the greater the surface exposed to the solvent action of the water, and hence the object of mincing meat thoroughly which is to be used in the preparation of beef tea. If such minced meat has been soaked for a long time in cold water, a part of the albumin and the extractive materials are obtained in solution, but the meat which is left is colourless, tasteless, and unpalatable; in fact, animals fed upon it soon deteriorate in strength.
The manner in which stewing differs from other processes of cooking is well described by Williams, who says: "Instead of the meat itself surrounding and enveloping the juices, as it should when boiled, roasted, grilled, or fried, we demand in a stew that the juices shall surround or envelop the meat." And more or less water enters the substance of the meat to replace the juices which have passed out by osmosis and diffusion into the surrounding fluid. After meat has been stewed for some time a scum containing a little coagulated albumin and more or less fat is usually seen floating upon the surface. This is usually removed in the preparation of beef tea for invalids in order to make it more palatable and more agreeable to the eye, but its removal is at the expense of considerable nutritious material. In the preparation of extracts of meat, such as Liebig's Extractum Carnis, the scum is removed before the solution is concentrated by evaporation.
Stews which are simply made in the manner described above, and which consist largely of meat and plain sliced vegetables, are fairly digestible; but if other materials or rich sauces are added to them, this is not the case, and if saturated with fat, they are quite unfit for invalids. As both the solid substance of the meat and vegetables and the fluid materials which have been extracted from them are eaten together in the stew, this is an economical form of preparing food. Nothing is lost by evaporation, and nothing is thrown away.