The Aroma of old wine is more agreeable, being largely due to ethers which are formed by a combination of the alcohol with the acids, and because the other aromatic principles are no longer masked by the carbonic acid which is disengaged when the wine has been recently fermented.
The Difference in Flavor is due to several causes, such as the loss of a great part of the mineral and vegetable salts, which have become insoluble by combination with the tartaric, acetic, and malic acid, and their consequent precipitation, and also to the deposit of a portion of the coloring matter.
So that when a wine is old, having been well cared for, it contains less coloring matter, vegetable and mineral salts, acids free and combined, tannin, ferments, mucilage, alcohol, etc., than when first fermented.
Influences which Develop, also Destroy.—Pellicot, quoting Béchamp, says that a wine ages and improves under influences analogous to those which spoil it, and he, himself, carries the idea a little farther, and adds, that the influence which produces the amelioration in a wine—which ages it—will, after having brought about the improvement, cause it to deteriorate, unless its action is opportunely suspended.
It must also be understood that certain influences which will greatly improve a strong, alcoholic, or a sweet wine, might in a short time entirely ruin a weaker one, or a dry wine.
Influence of the Air.—When a wine of ordinary strength, a table wine, comes into immediate contact with the air, a portion of its alcohol evaporates, it loses its bouquet and flavor, and if long exposed, a whitish scum is formed on its surface, called flowers. These have already been described in the chapter on fermentation as micoderma vini and micoderma aceti. A disagreeable flavor is communicated to the wine which the French call goût d’ évent, and the wine is said to be éventé, or flat; and it becomes turbid, and loses its transparency. Sometimes when the wine still contains sugar the flowers are not formed, but a second alcoholic fermentation sets in, and it works. If the wine is not immediately freed from contact with the air, it acidifies, becomes pricked, and by degrees turns to vinegar. (See [Acetic Fermentation].) And if still longer exposed, putrid fermentation sets in.
Sweet wines, whose alcoholic strength exceeds 16 per cent., and which contain a good deal of sugar, are not so liable to be injured by the influence of the air. Not only does their high degree of spirit interfere with acetic and putrid fermentation, but an insensible alcoholic fermentation sometimes takes place, and the supply of alcohol is kept up. But in time, as the sugar disappears, the alcohol becomes enfeebled by evaporation, and then acetic fermentation sets in, as in the weaker wines.
In the sherry countries it is considered necessary that the wine should be exposed to the action of the air, and therefore the casks are not kept full, and flowers are considered a good sign. In a few instances, where the wines are strong enough to bear it, aging may be hastened by some exposure to the air, but great care must be taken that they are not left too long under its influence, or disorganization may ensue. It must, however, be laid down as an almost universal rule, that the casks must be kept full and well bunged. (See [Ulling].)
Variations of Temperature affect wines like other liquids by contraction and expansion. When a full cask is put in a cold place, the wine contracts and leaves a vacant space; then it must be filled up or the wine drawn into a smaller cask. If the temperature of the wine in a full cask is raised, the liquid expands, and is apt to cause leaks; the sediment is liable to rise and give the wine a flavor of the lees.
Influence of Heat.—Guyot says that the higher the degree of heat to which wines are exposed, the greater their internal activity. Those subjected to 15, 20, 30 degrees, Celsius, (59°, 68°, 86° F.), sooner arrive at maturity, if young, at old age, if ripe, and at decrepitude, if old, than they would at a temperature of 10° C. (50° F.) From which the conclusion is drawn, that wines which have nearly or quite reached their maturity must be protected from heat, or at least from that of an elevated temperature, and that old wines should be kept in as cool a place as possible.