A knowledge of the facts just mentioned enables us to comprehend the nature and object of the practices adopted empirically for the pre. servation of wine ; above all. of those which are requisite to prevent it passing into the state of acetic acid, to which the wines of northern countries, or poor weak wines, are most prone. Thus, the processes of racking, sulphuring, fining, mixing, bottling, and keeping in cellars the temperature of which is low, are obviously all directed against the occurrence of the acetous fermentation, as they are mostly inadequate to check the vinous fermentation, and indeed altogether unnecessary, since so long as the vinous fermentation is going on—that is, as long as the alcohol continues to be generated—the wine is gaining in quality. Once begun, the presence of atmospheric air is in nowise necessary for the continuation of the vinous fermentation ; in fact, the more thoroughly it is excluded the better, for while the vinous fermentation, by which the wine is ameliorated, goes on, the acetous fermentation cannot commence.
From the above facts, established in the main by Liebig, it appears that while the azotised matter (gluten) iu grapes, wherever grown, is fixed quantity, the acids and saccharine matter are variable. When there is more saccharine matter, as in Itivesaltes, Frontignan, and Tokay, than there is gluten to hailstorm into alcohol, a portion of undeemnpoited sugar remains, sufficient not only to give that taste which has &clinked for them the name of neat wince, but also to exert the usual preservative power of sugar, when present in large quantities, and resist decomposition. Thus, Muscadine wine has been kept two hundred years; Mountain, buried at the time of the Fire of London, and disinterred in 1811, was excellent; and old Tokay, called nine Tames°, is In perfection at the end of a century. 'Ills wine needs neither aulphunng nor fining (Schema, Ungarna Weinbau,' order hand, p. 75); the casks are hermetically bunged ; and the reason Is obvious. To the juice of grapes grown in colder climates or cold seasons, sugar, especially starch-sugar, is added at the beginning of the fermentation. in order to consume all the leaven. Also to wine which it is apprehended Is about to become sour, or pricked, as the first sign of its becoming acetified is termed, sugar is also added ; but if vinegar has really been formed, this introduction of sugar, so far from hinder ing. only hastene the further transformation, as the presence of vinegar
Is the moat powerfully disposing agent to this change.
The odoriferous principle, or bouquet, of wines. appears to be due to peculiar ethers, or ETHEREAL SALTS. and, according to W'inckler, to combinations of volatile fragrant acids with a nitrogenous base of balsamic odour. The conditions of the formation and of the decom position of these compounds are not very well understood at present; some of the ethers, however, can be formed artificially.
The Intoxicating quality of wine Is, of course, due to the alcohol, the cause of the production of which has already been described. The method of ascertaining the amount of alcohol present in any sample, and a table showing the centesimal proportions of alcohol in various wines, will be found described under Asconotonernr.
F,ee acids, or acidulous salts, are present in most wines. Malic, tartaric, and citric are commonly met with. Port wine contains tannic acid, and the briskness of effervescent wines is due to carbonic acid. This natural acidity of wine must not be confounded with the sourness which wine sometimes aoquires, and which is due to acetic acid, gene rated by oxidation of alcohol, as already described.
The colouring smatter of wine is derived from the husk of the grape. If wine be prepared from the expressed juice only, it will have little or no colour. as in the case of Champagne ; but if the skin be also present, its colour will go into solution dining the process of fermentation, and will give the characteristic tint to the resulting wine. The presence or atsence of the purple skin, therefore, and not the colour of the grape, as popularly supposed, determines the colour of wine.
The chief seine constituent of wine is bitartrate of potash, or wine stone, or or, et, as it Is technically termed. It is the commercial source of tartaric acid, and has already been treated of in detail. [referent° Wines are much adulterated. For the English market they are commonly " fortified" with brandy, and superior varieties are fre quently diluted with those of inferior quality. Elderberry juice, called Cheripigo, also the juice of Phytolacen derandra, boiled mint, and burnt sugar are used for colouring; kind and logwood are used for the same purpose, and to augment the astringency of port wine; and occasioually artificial ethers are added to give flavour.