The mineral kingdom is not unrepresented in must, and certain saline substances are found in it. Of these, the salts of potash are uniformly present, and the most important is, without doubt, the acid tartrate of potash. This is the salt so well known in commerce under the name of cream of tartar. The lees of wine contain it in considerable quantity, and it is also found as a crystalline deposit in the inside of the casks. As the alcohol begins to develop in the must this salt is precipitated, and the more so the lower the temperature. Thus it is that a light wine of low alcoholic strength, if it be markedly acid, will lose the acidity in a cool, underground cellar. And, as a matter of fact, the proper maturation of a wine is impossible without a due amount of tartar; besides this, it develops in the wine a well-defined vigour and tonicity, which improves its taste, while it also increases its alimentary qualities.
There are a few other ingredients in must, namely, the colouring matters and essential oils, and the albuminoids, or nitrogenous substances. The colouring matters and oils appear to be contained in the cells of the inner side of the skin. Of these, the purpose of the colouring matter is obvious; while the essential oils are believed to contribute to the “aroma” of the wine. The albuminoids or nitrogenous substances are of the nature of white of egg; and, when in small proportion, are necessary for the due performance of the fermentative process. But, in excess, they are a source of considerable anxiety to the vigneron, in that they are the cause of much of the wine going wrong.
THE MAKING OF WINE—FERMENTATION.
The must, as we have already seen, is the juice of the grape, which has been squeezed out by the grape-mill or from the wine-press. The murk, or pomace as it is called in America, on the contrary, is the mass of grape skins, stalks, &c., left behind in the press. A clear apprehension of these two terms is required in order that no confusion may arise. The fermenting-vat is the cask in which what is called the strong, stormy, or tumultuous fermentation takes place. The “cuvage” is the length of time the contents are left in the fermenting-vat.
The whole phenomena of fermentation are too complicated and profoundly scientific to be dealt with here. I shall do no more, therefore, than briefly refer to the behaviour of the must in the fermenting-vat. Fermentation sets in soon after the must is placed within the latter. The germs of vinous fermentation are contained in abundance in the air of the wine cellar, as well as being on the grapes themselves. M. Pasteur, who has contributed so much to a proper understanding of fermentation, has proved that the yeast fungi come from the external surface of the grapes, and are not derived from the interior. Hence it follows that the skins are to be well crushed before fermentation begins, to ensure proper action in the must.