Wine is fermented grape-juice. The quality of wine depends upon many conditions. Some of these are: the variety of grape used, the soil and climate in which it is grown, its culture, and the character of the ferment that is employed in the manufacture of the wine. In recent times bacteriology has solved many of the problems with which wine-makers were formerly struggling. Pure cultures of various yeasts are used, and sometimes combinations of them, in order to produce the flavors that are sought for in wines. The sugar in grape-juice is more or less completely decomposed by fermentation, producing thereby varying amounts of alcohol. Its more or less complete fermentation depends in part on the amount of albuminous matter in the grape-juice. The yeast lives upon the albumin, but during its growth breaks up the sugar. If a given grape-juice is rich in albuminous matter, all the sugar may be fermented, and a 'dry' or sour wine may be the result. If it contains little, the wine will be sweet. The character of wine is often modified by the addition of alcohol or sugar. Natural wine cannot contain more than from 15 to 16 per cent, of alcohol, as yeast-cells are paralyzed by it when this percentage is reached. 'Fortifying' or adding alcohol to wine is a common practice. It is done both to flavor it and to prevent all further fermentation in it. Sherries are always fortified; so are most champagnes, especially the sweeter ones.

The details of wine-making vary greatly and cannot be described here. The character of individual wines depends much upon the methods employed in their manufacture. Some are made from the juice squeezed from the grapes under high pressure; others are made by fermenting the juice with more or less of the skins and seeds in it. To some grapes, lime is added when they are crushed. So much to illustrate the very numerous modifications that are adopted by wine-makers in the production of this beverage. The most important ingredients of wine are water, alcohol, acids, sugar, ethers, extractives, and glycerin.

Wine contains several alcohols. Ethyl is the one that occurs in the largest amount; amyl, propyl, butyl, and others are developed in it in smaller quantities. A wine containing more than 15 per cent, of alcohol is fortified.

The most important of the vinous acids are tartaric and tannic. A number of others are sometimes present. Acetic acid is not uncommon. The total amount of acid varies, but is often considerable.

Sugar occurs in wine in too small a quantity to be of much value as a food. The sweet wines contain about 4 per cent, of sugar, and the sour ones 1/2 of 1 per cent., or thereabouts. If wine were taken in sufficient quantity to obtain from it more than one-half or perhaps one-third of an ounce of sugar, it would produce intoxication.

The ethers result from the action of alcohols and acids upon one another. The flavors of special kinds of wine depend largely on the character and relative percentage of the contained ethers. They are very numerous, but each one occurs in very small percentage in any given specimen of wine. The extractives are mostly such carbohydrates as pectins and gums. Glycerin is always present in wine, but in very small proportion.

The following table from Dupre's analyses will give some idea of the chemical composition of a few wines that may be regarded as types of larger groups:

Cider, which is made from apples and pears, is very similar to wine. It contains from 3 to 8 per cent, of alcohol, from 0.2 to 0.6 per cent, of sugar, and 0.1 to 0.6 per cent, of acid. The chief acid present is malic.

Sparkling wines and ciders are bottled before fermentation is checked, and filled with carbonic acid gas by its continuance. When uncorked, the gas escapes in bubbles. This is called 'natural sparkling.' Artificial sparkling is produced by forcing carbonic acid gas into wine, as into soda-water. Effervescence adds to the attractiveness of wine, modifies its taste, and is said to hasten the absorption of alcohol from the stomach.

Wines check the chemical processes of digestion more than can be accounted for by the alcohol they contain. One per cent, of sherry will stop salivary, gastric, and pancreatic digestion. It is probable that the acids in wines, and possibly also some of the ethers, increase the inhibiting influence of alcohol over digestion. Sherry and port are more active in delaying digestion than claret, and much more so than champagne. Although they exert this deleterious influence upon the chemical processes of digestion even when they are taken in small quantities, they often improve appetite and stimulate more vigorous gastric peristalsis. Large amounts lessen nervous and muscular excitability.

A person leading a sedentary life cannot with safety take as much wine as one who is doing hard muscular work. Accepting as a just estimate the statement upon an earlier page that two ounces of alcohol is the limit permissible in health, one bottle of claret that contains approximately this amount is all that should be taken in a day, and not to exceed half of this amount of the stronger 'fortified' wines, such as sherry. Taking different kinds of alcoholic beverages at a time, or even during one day, interferes with digestion more than the drinking of one kind does. Wines are used in health chiefly because their flavor is agreeable and their milder effects upon the nervous system, such as lessening sensibility to worries and nervous tension, are grateful.

Their habitual use often produces sour stomach. Sometimes their excessive use causes gastritis. When those who are disposed to lithemia, gout, or rheumatism drink wine habitually, and sometimes even when they drink it only occasionally, they become especially liable to outbreaks of these maladies. It is not probable that the alcohol in the wine is the only or the chief cause of this. The acids and the sugars in it must also be blamed. For although the organic acids form in the blood alkaline salts which theoretically should do good, especially in cases of uric acid calculi, it is probable that the presence of acid wines commingled with food, and especially with sugar and starch, delays digestion, and permits the occurrence in the contents of the stomach of changes that produce the chief toxic principles. The ill-effects of these beverages are usually not felt by persons of the class under consideration immediately after drinking, but in from twelve to forty-eight hours later.

The tannic acid in sour wines gives them a rough, astringent taste. Such beverages may lessen diarrhea and aggravate constipation.