The different berries contain, as a general rule, a larger proportion of free acid than stone-fruit or apples and pears; and their acidity is the more obvious to the taste from their containing relatively small quantities of gum and pectine. The following remarks on some of our common varieties of fruits are of practical value.
In gooseberries, we recognize an agreeable proportion between the sugar and the acid, the ratio being as 6 to 1 in the sweeter kinds, and 4 to 1 in less sweet varieties of this fruit. The yellow kinds are far richer in soluble ingredients than the red.
Currants are so acid to the. taste, that they are almost always eaten with sugar; the ratio of the sugar to the acid being about 3 to 1, In strawberries, it is the aroma that we chiefly prize. The ratio of the sugar to the acid varies with the season and the species from 2 to 1 to 6.7 to 1 (in the pine-apple straw berry).
A similar remark applies to raspberries. In wild raspberries, the ratio is as low as 1.8 to 1, while in cultivated kinds it is as high as 3.5 to 1.
Grapes exceed all other fruits in their amount of sugar, which is seldom less than 12, and sometimes reaches 26 per cent. In good kinds, and in favorable seasons, the ratio of the sugar to the acid is as 29 to 1; in inferior kinds, and in ordinary seasons, it is as 16 to 1; when the ratio falls to 10 to 1, the grapes are unripe and acid. In other fruits, this would be a high ratio, and they would be regarded as sweet. The anomally may be thus explained. In unripe grapes, the skins are very thick, and contain an extremely acid juice, which overcomes the sugar contained hi the interior of the berry The juice of such grapes is found to be far sweeter than the grapes themselves.
From their large amount of sugar, and from the fact that their acidity for the most part depends on the acid tartrate of potash, which is almost entirely precipitated from the. wine, grapes are incomparably superior to any other fruits in the preparation of wines; and in their fermentation, different varieties of ether of a delicate odor are formed, which, in association with volatile oils that are also present, communicate to the more valued wines their special bouquet.
The ratio of the acid to the sugar in the must (the expressed juice before the com mencement of fermentation) affords the best evidence of the season. Thus, in the very bad wine-year of 1847, the ratio was 1 : 12; in the better wine-year of 1854, it was 1 : 16; while in the good wine-year of 1848 it was 1: 24, the same kind of grape being experi mented upon in all the cases.
. Apricots and peaches consist almost entirely of juice, their solid constituents,' after the removal of the stone, being only 1 or 2 per cent. These fruits are esteemed both' for their juicy and tender flesh, and for their powerful but delicate aroma.
In apples and pears, we have an increased quantity of cellulose and pectine, and con sequently a relative preponderance of the insoluble constituents. The cellulose contri butes to the firmness or hardness of these fruits, while it is to the pectine that they owe their property of gelatinizing when boiled. The well-marked differences of taste, etc., presented by different kinds of apples and pears; are due to the very varying relations that occur between the acid, the sugar, and the pectine, to the greater or less abundance of cellulose, and to the varying nature of the aroma. For equal quantities of sugar,
pears contain less acid than apples. In the different kinds of dessert apples, the ratio of the sugar to the acid ranges between 12 to 1 and 22 to 1, while in cooking-apples it averages not more than 8 to 1.
The chemical changes which take place in the F. during the process of ripening are described in the article PHYSIOLOGY, VEGETABLE.
. Keeping of Fruit—Many of the finest fruits undergo very speedy decomposition ; and on this account, some of those most highly esteemed in the countries which produce them, have never become articles of commerce, and are only to be enjoyed—except in the state of jam or preservecltiring the season of their ripening. Decomposition takes place most rapidly when fruits are exposed to the air, and particularly to stagnant air, when there is any dampness about them, and when they are subjected to considerable or frequent changes of temperature. Grapes are imported into Britain from the south of Europe, packed in saw-dust. Unripe gooseberries are kept for making tarts in win ter, in bottles or jars, filled up with perfectly dry sand, saw-dust, bran, or the like, closely corked and sealed, after a gentle heat has been applied to expel moisture as much as possible, and placed in a moderate and equable temperature, which is some times accomplished by burying them to some depth iu the earth. A similar method may be employed many other fruits. Pears, the finest kinds of which are very ,apt to rot almost immediately after they reach their perfect maturity, may be kept for months in glazed earthen ware jars very closely covered, and placed in a cool airy situa tion, out of the reach of frost. The layers of F. arc separated by the used for filling up the interstices, and the pears of the same layer are likewise kept apart, that rottenness in one may not infect the rest, which, with every kind of F., is very apt to take place. Another method is to keep them in drawers, the temperature being care fully regulated. Large gardens are often provided with a F. room, in which shelves and drawers are allotted to the different kinds of fruit, A moderate and equable tem perature, dryness, and careful ventilation, are the principal requisites of the F. room. F. intended for keeping should be carefully gathered, when almost quite ripe, and all bruising avoided. Pears or apples shaken from the tree cannot be expected to keep so well as those gathered by the hand. Of all the succulent fruits produced in Britain, the apple keeps best, and is therefore most generally used. F. intended for keeping is sometimes sweated before being placed in the jars or shelves; being laid in heaps for a short timeetiryitig 'according to the kihd of R, and extending, in the case of winter-apples to a fortnight or more—that some of the juice may exude through the skin; but the propriety of this practice is doubtful. Some kinds of winter pears and apples' can scarcely be said to be ripened till after they are placed in the F. room; and medlars are not tit for use till they have a state of incipient decay.