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.
There is undoubted advantage in varying the different methods of cooking as well as of flavouring the food from time to time. Monotony of diet and of flavours lessens the appetite and fails to stimulate the digestive organs into activity. When a reasonable variety of food cannot be obtained, variety in cookery may be made to replace its advantages to a great extent. Every one is familiar with the effect on the appetite of an occasional change of cooks or of a meal served in unwonted surroundings. 19
It is not within the scope of this work to discuss the details of cooking for the sick. Miss Nightingale wrote that "a good sick-cook will save the digestion half its work," and invalid cookery should form the basis of every trained nurse's education. It is impossible here to do more than explain the theory of the chief methods of cooking and suggest occasionally their influence upon digestion. As a rule, twice-cooked meats are undesirable for invalids. They are apt to be drier and less nutritious and digestible than when fresh. In meat "hash," for example, the meat fibre is too much hardened. Such preparations are often made too greasy by recooking for delicate stomachs. The same statement applies to canned meats when warmed over, for they have been already cooked once in the tin.
It is undesirable to combine foods which require different periods for their thorough cooking. For example, soup needs less boiling than the vegetables added to it, and they should be partially cooked alone beforehand, or they will be underdone.
The necessary heat for cooking is obtainable in many ways - from coal, wood, gas, oil, steam, and even electricity - and these different methods each possess advantages for particular foods.
Cooking, as a rule, at a prolonged low temperature is more economical in its results upon food than a much shorter application of high heat, and this is the theory of the famous "Count Rumford kitchen".