If the wine has already become acid, charcoal will not remove the flavor.
Sourness, Acidity, Pricked Wine—Causes.—Acidity is a sour taste caused by the alcohol of the wine being in part changed to acetic acid by the oxygen of the air. It is due to long contact with the air, and it is the oxygen which produces the change, as described under the head of Acetic Fermentation, and it is the more rapid, according as the temperature is more elevated, and the wine contains more ferments.
What Wines Liable to.—All wines whose fermentation is completed, and which have been fermented under ordinary circumstances—that is, those which have received no addition of alcohol, and no longer contain saccharine matter, are subject to this affection when left exposed to the air.
When they have been fortified up to 18 per cent. of alcohol, whether sweet or not, they do not sour until the alcohol has been enfeebled by evaporation.
If they contain sugar, although not fortified, a new fermentation takes place, and they do not acidify until the greater part of the sugar has been transformed into alcohol. Machard, however, says that wines which contain a good deal of sugar do often acidify, and in the experience of others, there is a continuous fermentation, which renders them very liable to become pricked.
As the acetic acid is formed at the expense of the alcohol, the more the wine contains of the former the less will it have of the latter.
Acidity is Prevented by giving wines proper care and attention, and by keeping them in suitable places, and by using the precautions indicated for flat or flowered wines, i.e., by avoiding long contact with the air. Flowers are the forerunners of acidity; yet they do not always appear before the wine is pricked, especially if the temperature is elevated, and the alcoholic strength considerable. In general, wines become pricked without producing flowers when they are exposed to the air at a temperature of 77° to 100° F.; acidity is produced under these conditions in a very rapid manner; and this is why extra precautions should be taken during hot weather. It should also be remembered that this vice comes either from the negligence of the cellar-man to guard the wines from contact with the air, or from the bad state of the casks, and storing in unsuitable places.
Treatment.—Acetic acid in wine may be in great part neutralized by several alkaline substances; but, if used, there remain in solution in the wine certain salts (acetates and tartrates) formed by the combination of the acetic and tartaric acid with the alkaline bases introduced. These alkaline substances not only neutralize the acetic acid, but also the vegetable acids contained in the wine. These neutral salts are not perfectly wholesome, being generally laxative in their nature. Moreover, the acetic acid cannot be completely neutralized by the employment of caustic alkalies (potash, soda, quicklime), and these bases decompose the wine and cause the dissolution and precipitation of the coloring matter, and render it unfit to drink by reason of the bitterness which they communicate. It is necessary, therefore, to choose for the treatment of pricked wines, those alkaline matters which are the most likely to neutralize the excess of acetic acid without altering the constitution of the wine, without precipitating their color, and which produce by combination the least soluble and least unwholesome salts.
Those which should be employed in preference to others are, carbonate of magnesium, tartrate of potassium, and lime water.
The following substances should only be employed when it is impossible to obtain those last mentioned, for the reason that the salts remaining in solution in the wine may cause loss of color, and even decomposition, if used in large doses, i. e., wood ashes (ashes from vine cuttings being preferred as containing much of the salts of potash); powdered chalk and marble (composed of the sub-carbonates of lime, marble dust being the purer); solutions of the sub-carbonates of potash, and of the sub-carbonates of soda, and plaster.