The actual substance—ferment—which causes the breaking up of sugar into alcohol and carbonic acid, has been submitted to careful chemical and microscopical examina tion. One hundred parts of sugar require about 1.5 parts of ferment reckoned in the dry state; and as the analysis of ferment shows that about half of it consists of albumin. ous matter, it follows that I of a part of albuminous matter are required for the conver sion of 100 parts of sugar into alcohol and carbonic acid. Ferment consists of cells or globules of torula (q.v.), which are precisely the same in the production of wine and beer. It is the contents of these cells which contain the active albuminous matter; while the cell-wall, consisting of cellulose, and produced from gum or vege table mucus, is inert.
The leading points in which the constituents of grape-juice and those of wine differ i from one another in consequence of fermentation are, that in the wine there is a diminu tion (1) of the mucilaginous and saccharine matters, iu consequence of the formation of ferment and alcohol ; (2) of those substances which are insoluble in common water, but are held in solution in the viscid must, as, for example, phosphate and sulphate of lime; and (3) of cream of tartar, tartrate of magnesia, and sulphate of potash, which, being less soluble in spirit than in water, fall as the formation of alcohol increases. Red wines lose a portion of coloring matter and of the tannin, which is withdrawn by these salts, and hence 1kt:erne of a lighter color and less astringent. Before noticing the alcoholic strength of different wines we shall briefly describe the concluding steps necessary for rendering wine fit for use. The process of clearing is undertaken with the view of removing all the sediment in which albuminous matters may still occur, and of dimin ishing the coloring matter and tannin of red wines. Among the substances used for these purposes may be mentibned albumen, isinglass, gum, milk, lime, gypsum, etc. In warm countries gum is preferable to albumen or isinglass. The addition of lime throws down a precipitate of salts of lime, which carries down, in the case of red wine, a con siderable quantity of coloring matter; its addition gives a sweeter and less astringent taste to the wine, and an appearance of age. As a general rule clearing increases the durability of wine. Sulphurizing is a process which is especially applied to sweet white wines which possess an excess of sugar and albuminous matter, and little tannic acid, and thus become easily decomposed. Its object is to check undue fermentation, and to prevent, the formation of mold, which afterward imparts a musty taste to the wine. The process is effected by burning sulphur in bottles or casks, and instantly pouring in the wine, which absorbs the sulphurous acid. Wine intended for exportation to warm climates is usually strongly sulphurized. Of course great care must be taken that the sulphur is free from its common impurity, arsenic. In place of sulphurizing, another method of hindering the fermentation of sweet wine is adopted in some parts of France; it consists in putting part of powdered mustard into the wine; but how it acts is unknown.
Having traced the chemical history of wine from its original state of grape-juice to the time when, having been clarified, and poured into casks and bottles, it is fit for use, we ought, in order to complete the sketch, to notice the subsequent changes which, in the course of time, it undergoes in the cellar. • The ages at which different wines attain their perfection are, as is well known, extremely different. " As a general rule," says Mulder, "wines which have retained a considerable portion of albuminous matter, and possess but little tannic acid, cannot resist the influence of time; they become acid, or undergo some other change. This occurs in the case of Rhine wines,which contain but
little alcohol; and all those wines which contain much sugar, or but little tannic acid, cannot be kept long. Wines which can be eellared are those which improve; or, to speak more correctly, those wines are stored which improve with age. In these odor iferous substances are formed, and the wine becomes less acid and better tasted. Such me as is colored often deposits a considerable amount of sediment; and if it be stored in casks there is a constant increase of alcohol."—Op. cit., pp. 105, 106. Wine is improved by being kept in wooden casks, as water escapes by evaporation, and the other constituents are relatively increased. The vinous constituents being thus con centrated exert a stronger chemical action upon each other, and render the wine not only stronger, but better flavored. The change, however, does not stop here. The loss of water must be replaced by the addition of wine, otherwise the action of the air would turn the wine sour, and convert the alcohol into acetic acid; and the diminution i of which is thus replaced by wine, causes a constant increase of tartaric acid. Wines which are poor in sugar may thus soon become too sour; and consequently all wines cannot undergo this process. The popular idea that wine which has grown old in bottles has therefore become richer in alcohol is altogether false, and is doubtless founded on the fact that it is only the strongest wines that can be preserved. The color, however, of bottled wine is materially affected by age: liqueur-wines and red wines containing no large amount of tannic acid becoming darker, while wines which are rich In tannic acid, as port, for example, deposit a sediment, and become lighter. Old bot tled wines contain odoriferous constituents—ethers of various organic acids—which arc not found in new wine. For an explanation of the mode of formation of these com pounds, to which wine owes its aroma, we must refer to the chapter on " The Odorifer ous Constituents of Wine" in Molder's work; we will here merely remark that diminu tion of the free acids is necessarily associated with the formation of these compounds, and that this diminution can only occur by the acids being either decomposed or com bined with non-acid substances, both of which operations here take place as the result of a very slow chemical process. This effect of time may, however, be imitated by art; and if bottles corked, but not quite tilled with wine, are placed for two hours in warm water at a temperature of 185", and after cooling are filled, their contents pos sess the flavor and aroma of wine that has been bottled several years. This result was originally obtained by Appert; but Pasteur and others have, during the last few years, again brought the subject before the French academy. Wines which have been long in bottle sometimes acquire a peculiar flavor, which is incorrectly referred to the cork. It is in reality due to the peculiar mold which grows from the outside of the cork inward; and should it reach the inuer surface, it imparts to the contents of the bottle a peculiar taste; and this Wine is said to be corked. Very similar to this is what is known as "the taste of the cask," a peculiar flavor sometimes acquired by wine before bottling. This flavor is regarded as dependent on the development of a peculiar essential oil, during the growth of " mold" on the surface of the wine. It can be removed by the addi tion to each pipe of about a quart of olive oil, which dissolves the unpleasant flavoring matter, and carries it to the surface.