Many ordinary wines possess while young, if they have been well made, and are produced in favorable years, a marked fruity flavor; but in the greater part of the wines of this kind, this mellowness does not last, and disappears gradually with age, while in the grand wines of good years, the unctuosity is more appreciable after the defecation of their lees than while they are new.
The substance which in a measure produces this quality is called mucilage by Maumené and some others. Others, again, have given it different names. Maumené says that it seems to be a sort of intermediary substance between cellulose and dextrin, and that its nature is not yet known, but that it is a near neighbor of sugar.
Mr. Boireau believes that the mellowness is produced by a modification of grape sugar, because, when not properly cared for, mellow wines undergo an insensible fermentation, especially if they are in their first and second years, and still contain ferments. Very often at the end of these secondary fermentations, the unctuosity has disappeared, and the wines have become dry. It seems, accordingly, that the substance is capable of undergoing the same transformations as sugar under the influence of ferments and heat.
Pectose is found in green grapes and other fruits, and by the acids is changed into pectin, which is the gelatinizing principle, is soluble in water, and may have some effect on the mellowness of wine. Alcohol precipitates it in the form of jelly.
Fatty Matters have been found in wine lees, which may be extracted from the seeds by long contact during fermentation, for it is known that the seeds yield such matters.
Glycerin is mentioned among fatty matters, but it is known to be produced by the fermentation of sugar, and is supposed to have its influence on the flavor of wine.
The Coloring Matter of red wine has received the name of œnocyanine. In its pure state it is blue, but is changed to red by acids. The yellow and brown color of some white wines is due to the oxidation of some of the matters contained in them. The change of color in red wines is also due to the oxidation of the tannic acid, thereby forming an insoluble compound, tannomelanic acid, which is precipitated, carrying down the œnocyanine, and the wine gradually becomes tawny.
Aldehydes are produced first in the transformation of alcohol into an acid by oxidation, acetaldehyde occurring between alcohol and acetic acid, as mentioned in Acetic Fermentation. When a weak wine is exposed to the air it is gradually converted into vinegar, or acetic acid. If free access of air is permitted, it may be converted at once into acetic acid, but if the access of the air is very limited, or if the wine is rich and strong, oxidation stops at the first stage, and aldehyde is formed. It is a colorless liquid of a very suffocating smell, having an etherous odor, and is supposed to have an important influence on the flavor and bouquet of various wines. The strong wines of southern countries which are kept in casks in ullage, exposed to the action of the oxygen of the air, develop a certain amount of aldehyde in time, and it is supposed that sherry owes some of its qualities to this substance.
Acids.—We can only allude briefly to the acids which have been recognized in wines. The principal one is tartaric acid, found in considerable quantities in grapes, and is contained in the argols, or crude cream of tartar, bitartrate of potash, which is deposited on the inner walls of the casks in which the wine is kept. This substance principally gives the acid taste to wine.
Malic Acid, or the acid of apples, is found; and of citric acid, or the acid of lemons, traces have been recognized; also pectic acid, derived from the pectose.