Besides the water and the glucose, the must likewise contains quite an appreciable amount of those important bodies, the various acids. These consist of tartaric acid, so frequently met with all through the vegetable world; of malic acid, which is the acid almost distinctive of apples; of tannic acid or "tannin," and of other acids. These different acids play an important part in the production of wine; without them, in truth, it would be a mere admixture of spirits and water—a colourless, flavourless, and insipid product. By their assistance, however, wine is endowed with the brilliancy it possesses. And more than this, the action of the alcohol on these acids develops those exquisitely delicate ethers—the oenanthic and other ethers—which constitute, in fact, the bouquet of the wine. At the same time, it has also to be remembered that while these many acids constitute the life and soul, so to speak, of the wine, their very presence is absolutely necessary for the process of vinous fermentation. That is to say, the active agents of vinous fermentation are only enabled to work perfectly in a liquid which is somewhat acid.
There is an astringent principle, named tannin, which calls for attention in any reference to wine-making. It is almost the same body— not quite—as the tannin obtained from galls, and so largely employed in tanning. This vine-tannin, if it may be so termed, does not exist in the juice of the grape, but in the stalk and the skin. The white wines, in which the juice is almost always freed from the skins and stalks, contain but little tannin; while, on the contrary, most red wines, in which juice, skins, and stalks are all included together in the fermenting-vat, contain a good deal. Some white wines derive their tannin from the oaken casks which hold the wine; and their colour, in consequence, subsequently deepens. Other red wines, strange to say, gradually lose their dark colour from a certain action of the tannin. So that tannin is the cause of some white wines deepening in colour, while it renders other red wines of a lighter colour. Now, tannin has the effect of preserving albuminous substances, and in this way it may be beneficial in rendering red wines more durable. But although this may be advisable in wines which are liable to turn, it is certain that excess of tannin is most undesirable. In fact, the practice of placing the stalks in the fermenting-vat is in many cases, as I have previously stated, an unnecessary proceeding.
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.
The temperature of the must soon begins to rise, and the fermentative agencies break up its glucose into alcohol and carbonic acid gas. There is a bubbling and seething in the liquid during this action, which gradually subsides. The increase of temperature in the fermented fluid begins to abate; the skins and husks subside to the bottom of the vat; the liquid itself becomes slightly less turbid—and the first stage of wine-making is at an end.
A clearer insight into this important part of the process will perhaps be gained by noting some of the practices followed on the Continent, as regards the duration of the vattage. The length of time the various contents—whether they be the grape juice alone, or the grape juice together with the skins and stalks—remain within the fermenting-vat, varies greatly in different parts. In the Champagne country, the must is allowed to stand for twelve or eighteen hours, during which time a froth arises to the top and a sediment descends to the bottom. Without disturbing either of these, the precious liquid is carefully withdrawn into small barrels, and the fermentation is then allowed to proceed. This purification is one of the most important matters connected with the making of champagne.
The Medoc districts, in the Bordeaux territory, produce the finest of the clarets. The grapes are detached from the stalks, and subjected to pressure. The must is put into the fermenting-vat, to which is added the murk resulting from the pressing, and the stalks which were previously separated from the berries. The time necessary for vinification varies; in good years it is no longer than four or five days, and the future wine will then be at its best with regard to taste, delicacy, and softness.