Sourness—Its Causes.—Sourness, or heated flavor, as it is also called, is due to the presence of acetic acid in the wine. All wines, even the mellowest, the best made, and the best cared for, contain some acetic acid, but in so small a quantity as to be inappreciable to the taste. Acetic acid is produced in wines during their fermentation in open tanks, and is due to the contact of the air with the crust of the pomace. This crust or cap, formed of skins and stems, brought to the surface by bubbles of carbonic acid rising from the liquid, is exposed directly to the air, and the alcoholic fermentation of the liquid part is soon completed, and under the influence of the air and ferments, the alcohol is transformed into acetic acid. This transformation is so rapid that when the vatting is too prolonged, and the temperature is high, the exterior crust rapidly passes from acetic to putrid fermentation.
As long as the tumultuous fermentation continues, the crust is kept up above the surface by the bubbles of rising gas, but when it ceases, the cap falls, and settles down into the liquid, and the wine becomes impregnated with the acetic acid. The wine also, by simple contact with the crust, acquires a vinegar smell and taste.
Wines which become pricked by contact with the air after fermentation are treated further on under the head of Pricked Wines.
How Prevented.—The formation of acetic acid during fermentation is prevented by fermenting the wines in closed or partly closed vats, by avoiding contact of the air, by keeping the pomace submerged, and by confining the carbonic acid in the vat. If open vats are used, they should be only three-fourths full, so that a layer of gas may rest upon the pomace and protect it from the atmosphere; or the cap may be covered with a bed of straw as soon as formed. Care should be taken to draw off as soon as fermentation is complete.
Treatment.—Wines affected in this manner cannot be expected to acquire good qualities with age. They may be rendered potable, but their future is destroyed. Therefore, every precaution should be taken to guard against the defect. They should be separated from their first lees as soon as possible; consequently, they should be drawn off as soon as the gas ceases to rise. If they are still turbid, they should be clarified by an energetic fining, and they should be racked from the finings the very moment they are clear. They should be afterwards racked to further free them from ferments. If the wines are only heated, the odor of acetic acid will be sensibly diminished by the above operation; but if they are decidedly pricked, the means to neutralize their acid when drawn from the vat, as indicated for Pricked Wines, should be resorted to.
Alcoholic Weakness is due to a want of sufficient spirit, caused by an excess of water of vegetation, and the consequent lack of sugar in the grapes. In France this defect is generally found in wines coming from young vines planted in very fertile soils, or from the common varieties, pruned with long canes, and producing a great quantity of large, watery grapes. When wines weak in alcohol contain but little tannin and color, they rapidly degenerate, often commencing their decline during their first year, and before their clarification is completed.
How Avoided.—This defect can be corrected by planting the proper varieties of vines, and by avoiding rich soils; but in the climate of California there is but little danger of the wines being too weak, unless the grapes are late varieties, and grown in very unfavorable situations.
The Treatment of weak wines is to rid them of their ferments as soon as possible, in order to avoid acid and putrid degeneration, to which they are quite subject. This result is obtained by drawing them off as soon as the lees are deposited. If they remain turbid after the second racking, they should be gently fined with the whites of nine or ten eggs to 100 gallons. The coagulation of the albumen will be facilitated by adding one or more quarts of strong alcohol to the wine before fining, and by adding to the eggs a handful of common salt dissolved in a little water. But as these wines, by themselves, are short lived, it is necessary, in order to prolong their existence, to mix them with firm wines, strong in body and rich in color. By adding alcohol, they are still left dry and without fruity flavor, while if mixed with a wine of a flavor as nearly like their own as possible, and having a fruity flavor, and being firm and full-bodied, but not fortified, they will acquire mellowness as well as strength.
Want of Color—Causes.—As coloring matter is not found in the skins of grapes till they are ripe, green wines produced in years when the grapes do not ripen well, lack color.
The amount of color may be diminished if by excess of maturity the skins of the grapes decay.