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.