COMPOSITION AND ADULTERATION. The con stituents of grape must vary considerably in percentage with season, variety, state of ma turity. etc. The principal ones are water, sugar, and cream of tartar (hitartrate of potassium).
In cold climates, especially in unfavorable years, the sugars present (about equal parts grape and fruit sugar. with some cane sugar) may be less than twelve per cent.; in very warm localities, thirty per cent. or even more; the usual range is from fifteen to twenty-five per cent. Since they continue to form until the grapes are fully ripe. some is sacrificed when im mature grapes are used: and since the mature fruit loses moisture rapidly, the relative propor tion of sugars to water increases after maturity phenomenon utilized in making certain wines, notably Malmsey. In the preparation of dry wines, musts containing more than twenty five per cent, of sugar are commonly diluted thus to prevent the formation of a sweet wine by the non-conversion of the sugar into alcohol. Fer mentation does not yield more than about 14 per cent. of alcohol and is slow and uncertain above 12.5 per cent. It converts the sugars largely into alcohol and carbon dioxide, theoretically thus: Glucose or_ Carbon 11cohol+ levulose dioxide the alcohol being 51.11 per cent. of the sugar fermented. In practice, however, only about 4S.5 per cent. of alcohol is formed, the deficiency be. big represented mainly by glycerin (from 6 to 14 parts by weight to 100 of alcohol), higher alcohols, succinie and acetic acids and ethereal salts. upon the nature and quantity of which last the flavor of wine largely depends. Since the development of sugar is largely dependent upon temperature, the wines of northern mates are uniformly poorer in alcohol than those of the south. The alcohol content of unfortified wines known to be pure varies from to IS per cont. by volume; that of glycerol, from 0.2 to 1.4 grains per 100 cubic centimeters. A relatively high ratio of glycerol to alcohol is thought to indieate a superior wine, and in Europe a content of 7 to 14 parts glycerol to alcohol is desired, but, since many wines contain less than 7, the tendency is to lower the mm to 6. Judging from the few complete
analyses, American wines seem to fall below European in this ingredient.
Cream of tartar, to which the acidity of must is largely due, may range from 0.5 to 1.5 per cent. As grapes mature their relative acidity diminishes with the increase of sugar; as the must matures its absolute acidity decreases be cause of the deposition of cream of tartar, which is insoluble in alcohol. The acid of wines, which rarely contains less than 0.4 gram nor more than 1.5 grams, calculated as tartaric acid, per 100 cubic centimeters, is often diminished during ageing, by the action of microorganisms as well as by the separation of the cream of tartar. It. may, however, he increased by concentration and by the formation of lactic and suecinic acids. Its content is usually in inverse ratio to the tent of alcohol ; thus dry, northern wines are less alcoholic lint more acid and aromatic than southern ones. Volatile acids are always formed during fermentation. but excess indicates lessness in management. In northern wines they are limited to .12 and .16 grams per 100 cubic centimeters respectively, in white and rod wines, Coloring matter is found in the skins, which, like the stems and seed coats, contain tannin. the closer the crushing, and. in red-wine making. the longer the immersion of these parts in the must, the higher the percentage of tannin in the expressed juice. Tannin is not present in the 'first and, like coloring matter, is de ficient hi the juice of stemmed grapes quickly pressed.
Allmminoids, of which from 0,25 to 0.9 per cont. is found in must. :ire somewhat decreased by fermentation. Their deficiency precludes complete fermentation; their excess is to fere with the preservation of the wine; but their /alleys are not fully understood. Varying some wl at Nvith the varlet ies, tire solids of white wine (except sugar) vary from 1.6 to 2.5 grams per 1011 cubic centimeters: those of red wine.