The important ingredients in wines, from the medical point of view, are the following: -
There are in addition slight amounts of extractives, chiefly of a carbohydrate nature, and of glycerine, produced in the process of fermentation, but these are of little practical importance.
The amount of alcohol (ethylic) present in wines ranges from 8 to 11 per cent, or thereby in the case of natural red wines, to 20 per cent, or more in fortified wines, e.g. port. All natural wines are comparatively poor in alcohol, and thus readily undergo the acetic fermentation. A fortified wine therefore keeps better, subsequent fermentation being restrained. Amyl alcohol and other higher alcohols are present in traces even in sound wines. As is invariably the case when alcohol is formed by fermentation, carbonic acid gas is given off, and if a wine is bottled when this action is all over, the product is a "still wine "; if, on the other hand, the wine is bottled, like beer, before the fermentation is quite over, then the liquor becomes charged with carbonic acid gas, which effervesces or liberates, producing a "sparkling" wine. Sparkling wine may also be made on the principle of aerated waters,by passing carbon dioxide into the wine under pressure.
In a good wine the total acidity should be not more than 0.3 to 07 per cent. The taste of a wine cannot be regarded as a criterion of its acidity, as the acid may be masked by a high proportion of sugar. The acidity is due to natural acids and acids produced by fermentation. The natural acids in wine are tartaric, tannic, and malic acid. Tartaric acid exists in combination with potassium in the form of potassium bitartrate. As the proportion of alcohol in wine increases with age, the bitartrate becomes less soluble, and settles out in the form of "tartar." The tannic acid in wine is responsible for the astringent taste of certain wines.
Acetic, formic, succinic, and other fatty acids are produced in wines by fermentation. Red wines usually contain rather more of these volatile acids than white wines. If present in excess, the wine is slightly " turned," that is, on its way to become vinegar.
According to Dupre, the amount of acid, reckoned as tartaric, in a bottle of wine is as follows: -
Claret . 65 to 77 grains. Hock . 57 „ 70 „
Sherry . 54 to 61 grains. Port . . 49 „ 62 „
Marsala . . . 39 to 46 grains.
A natural wine should contain about 1/2 per cent, of sugar. Fortified wines may contain 2 per cent, or more, and sweet wines as much as 20 per cent. The following analysis is given by Dupre: -
1.4 to 8.6 grains per bottle.
11 " 18 " "
Sherry . .. .
217 „ 421 „ „
221 „ 519 ,,
Old Marsala ....
38S „ 451 „ „
125 " "
500 grains down to almost none.
The ethers present in wine impart to it its bouquet. The volatile ethers are derived from the volatile acids, eg. acetic acid; the fixed ethers are the product of the fixed acids, e.g. tartaric acids.