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.
Grapes are universally grown and enjoyed on account of their delicious flavour and aroma as well as their general whole-someness, and they constitute an important article of diet. Perfectly ripe and seedless grapes, such as the Black Hamburg and other varieties, have long been recognised as an excellent food for invalids. Grapes contain so large a proportion of water that they possess but little nutrient property, although they hold considerable sugar, but the salts which they furnish to the system are useful. These salts are the sulphates, phosphates, and chlorides of sodium, potassium, calcium, magnesium, and iron.
The habit which some people have of swallowing the pulp whole with the seeds, however small the latter may be, cannot be too strongly condemned. The seeds under no circumstances are digested, being too hard and tough to be affected by any of the juices of the digestive tract, and they therefore act as irritants or foreign bodies. It was originally believed that inflammation of the appendix vermiformis was often caused by the entrance of one or two sharp-pointed grape seeds into this small division of the alimentary canal, but this has been proved to be an exceedingly rare occurrence. The main disadvantage of swallowing seeds consists in their interference with normal digestive processes, while they are liable at any time to cause more serious disturbance of the nature of diarrhoea, enteritis, or intestinal obstruction. Swallowing the skins of grapes is equally harmful.
Grapes, on account of their sugar, must be excluded in cases of diabetes and gout. A special "grape cure " has been established for some diseases. It is discussed under that heading. Unfermented California grape juice constitutes an agreeable, wholesome, and slightly laxative, non-alcoholic beverage, which may be prescribed during mild fevers and in convalescence. Prof. Albert R. Leeds has recently sent me the analysis of a new grape food which he says "is entirely different from the grape juice, inasmuch as it contains, both in amount and condition, the constituents of the grape to a point of practical completeness which the manufactured juices have failed to attain. I have verified by most exhaustive tests the absence of all germs of fermentation, and this sirup will certainly keep indefinitely, even in the absence of alcohol or antiseptic." This "liquid grape food " contains protein and 64 per cent of grape sugar, with no alcohol and no starch.
Raisins, prepared by sun-drying from certain species of grapes which are particularly rich in sugar, form a useful food, chiefly on account of the agreeable flavour which they impart to more insipid substances. (See also Raisin Wine).
Raisins are usually made from white grapes, but they turn dark purple or brown from oxidation of the tannic acid of their skins (Leoser). Muscatel raisins are dried on the vine by incising the stems to cause withering of the grapes.
Raisins cannot be eaten very abundantly without disordering digestion unless they have been cooked. Added to some forms of farinaceous food - such as rice pudding, sweetened breads, buns, cakes, pemmican, and the like - they increase the appetite. If given to children, as they too often are, they should be stoned carefully beforehand, and the tough skins must not be swallowed. The latter contain a whitish waxy material which keeps the grapes waterproof.