PERMEN TATION. Since wine fermentation is due to yeasts found in the air nail upon the skins of the fruit, the addition of yeast to the must as in lN•er•mwking iv unneeessary. Action starts in from 12 to 3•t hours. upon the tempera litre. and continues briskly for abont a week. Selected yeasts (pure cultures), which htlye been carefully investigated, have been found of little value in cold climates, but in warm re gions they are of assistance in controlling fer mentation and improving the flavor of the fimb ished product. it is not true, however, that they can convert cider into high-grade wine as is popularly reported.
In making red wine the grapes may be fer mented whole or after crushing according to the vintner's preference. The former practice in sures a clearer, brighter wine than the latter, which yields a larger 'first run' (via de goutte) and a wine richer in body and coloring matter. In white-wine making the must beeomes turbid from the growth of yeasts in it and from the flocculation of proteids and tartar. During the fermentation of red-wine most the lhatting mass (cap) of skins, stems, etc., brought to the surface by the gas evolved must he thoroughly mixed daily with the liquid to prevent souring and to insure uniform fermentation. To avoid this lqbor, perforated or loosely fitting covers are used, and in making red wine diverse inventions for excluding the air are gaining in favor.
With the appearance of requisite color in the must, the mass is pressed. an operation which, depending upon the color of the grapes and their content of tannin, may occur the day after crush ing, usually before the fifth day, lint sometimes not until the conclusion of fermentation. Since rapid fermentation at temperatures above 25° C. produces less aromatic and less stable wines than slower action at lower temperatures—a fact which largely accounts for the superior aroma of northern wines—cool cellars have long been used and artificial methods of cooling are sometimes employed. As soon as the wine becomes clear,
usually in December, it is racked into clean casks and kept at a lower temperature in the sub cellar. Here a slow fermentation continues and a second racking (drawing off) is made in March or April. when cheap wines may be bottled for sale. Higher grades are kept in casks and racked annually (in some eases for eight years) until the sediment (tartar, proteids, gummy matter, etc.) ceases to form, the casks hieing kept full to the bung by additions of wine every week dur ing the first few months and fortnightly there after.
The fine bouquet so much desired is produced by the gradual oxidation of the alcohols and the combination of the resultant products with acids; hence the necessity of keeping the wine in wood, through the pores of which the air enters. No bouquet is formed in air-tight vessels. Racking every alternate month permits the absorption of oxygen, tints hastening the formation of bouquet. But it exposes the wine to possible infection of so-called diseases which may impart stale, sour, or hitter flavors and thus ruin the product. To obviate this, scrupulous cleanliness is imperative. As an additional precaution, however. antisepties and other means are used as preventives. Of these practices. burning sulphur in the casks is most general; filtering through unglazed porce lain, fining with gelatin and tannin are used in specific occasional cases; and pasteurizing has gained in favor since being demonstrated useful.