Cooking in water extracts so little of the nutritive material present in fruit that such removal of nutrition is of no practical importance unless the amount of water used is excessive. Because they contain much water fruits should be cooked in as little water as may be necessary to prevent them from burning. The idea is quite generally held that cooking fruit changes its acid content, acid being sometimes increased and sometimes decreased by the cooking process. Kelhofer showed that when gooseberries were cooked with sugar, the acid content was not materially changed, these results being in accord with his conclusions reached in earlier studies with other fruits. The sweeter taste of the cooked product he believed to be simply due to the fact that sugar masks the flavor of the acid. It is often noted that cooked fruits, such as plums, seem much sourer than the raw fruit, and it has been suggested that either the acid was increased or the sugar was decreased by the cooking process. This problem was studied by Sutherst, and, in his opinion, the increased acid flavor is due to the fact that cooked fruit (gooseberries, currants, plums, etc.) usually contains the skin, which is commonly rejected if the fruit is eaten raw. The skin is more acid than the simpler carbohydrates united to form a complex carbohydrate. In some fruits, like the apple, where the jelly-yielding material must be extracted with hot water, the pectin is apparently united with cellulose as a part of the solid pulp. As shown by the investigations of Bigelow and Gore at the Bureau of Chemistry, forty per cent. of the solid material of apple pulp may be thus extracted with hot water, and consists of two carbohydrates, one of which is closely related to gum arabic. That such carbohydrates as these should yield a jelly is not surprising when we remember that they are similar to starch in their chemical nature, and, as everyone knows, starch, though insoluble in cold water, yields when cooked with hot water a large proportion of paste, which jellies on cooling. When fruits are used for making pies, puddings, etc., the nutritive value of the dish is, of course, increased by the addition of flour, sugar, etc., and the dish as a whole may constitute a better balanced food than the fruit alone.[9] FOOTNOTES: [9] C. F. Langworthy, Ph.D.—In charge of Nutritive Investigations of the United States Experiment Station. CHAPTER VIII FOOD REQUIREMENTS OF THE SYSTEM As previously stated, the object of foods is: To supply the needs of the body in building new tissue as in the growing child. To repair tissue which the catabolic activity of the body is constantly tearing down and eliminating; and To supply heat and energy.