Wine is the fermented juice of the grape of _Vitis vinifera_. In its preparation, the fully matured grapes are usually (but not always) first separated from the stalks, and then crushed, the _marc_ so obtained being afterwards placed in butts provided with perforated sides, through which the expressed juice or _must_ percolates. It is next introduced into vats, and allowed to undergo a process of fermentation, which is very analogous to that of beer wort. The addition of yeast is, however, in this case unnecessary, as the fermentation of grape-juice is spontaneous, it being due to the generation of the fungus _Penicillium glaucum_, which is the product of the action of atmospheric germs upon the albuminoid matters contained in the must. The most important constituents of grape-juice are glucose (10 to 30 per cent.), organic acids (0·3 to 1·5 per cent.), and albuminous substances. During the fermentation the glucose is converted into alcohol and carbonic acid, the latter being evolved in bubbles; a deposit of potassium bitartrate and yeast-cells, forming the _lees_, likewise occurring. This first fermentation ceases after the lapse of several days, the period being indicated by the cessation of escaping gas. In order to prevent the oxidation of the alcohol to acetic acid, the liquid is removed from the lees and transferred into casks, in which a slow after-fermentation and a further separation of potassium bitartrate take place. The wine is subsequently stored for a considerable time in fresh casks, during which it “ages,” and acquires its characteristic flavour. The more common varieties of wine are classified according to the country of their production--into French (claret, burgundy, champagne, etc.), German (Rhine), Spanish (sherry and port), and Italian.