The basic ingredients of a completed wine are water and alcohol, though other components present in minuscule quantities account for quality and character. A list follows:
Water (80 to 85 percent) The water in wine derives entirely from grape juice, so it is biologically pure. It is the base for all the complex biochemical phenomena that occur as wine is made and aged.
Alcohols (10 to 17 percent) Alcohols in wine are attained by yeast-converting sugars. Besides adding their own characteristic flavors and odors, alcohols are the main carriers of aroma or bouquet. The most important alcohol in quantity is ethyl, a monoalcohol. Then comes glycerol, a polyalcohol that adds a degree of sweetness. Butylene glycol is among other polyalcohols and cyclic alcohols present. In some fortified wines, alcohol attained by distillation may be added.
Acids (0.4 to 1 percent) Acids give wine the sour or sharp aspect that enhances flavor when in balance with other components. Of the three organic acids that originate in grapes, tartaric is prevalent as the base measure of total acidity in wine, followed by malic and citric. Three other acids - succinic, lactic and acetic (source of volatile acidity) - are produced by fermentation.
Sugars Grapes contain 15 to 25 percent glucose and fructose, sugars that are mainly converted to alcohol through fermentation. In dry wines a trace of residual sugar (0.1 percent) is normal, sweet wines may contain them at up to 10 percent. A wine's sweetness is derived not only from sugars, but also from alcohol and other substances.
Mineral salts (0.2 to 0.4 percent) Salts derived from mineral acids or organic acids lend freshness to the flavor of wine. Among them are potassium, sodium, magnesium, calcium and iron.
Flavoring and coloring substances (0.01 to 0.5 percent) Phenolic compounds give wines color and account for differences in flavor between reds and whites. Grape skins contain polyphenols in the form of anthocyanins and tannins whose pigments give red wine its color. White wines derive a little color from grape skins, as well as from wood and aging.
Odorous substances Traces of diverse chemical compounds of a volatile nature account for certain odors in wine. These include alcohols, aldehydes, esters, acids and ketones.
Sulfites Sulfur derivatives are used to safeguard grapes and sterilize and preserve wines. The presence of sulfites at 10 to 200 parts per million (the upper limit for Italian wines) is measured both in fixed sulfur dioxide, combined with other substances, and free sulfur dioxide in the form of gas.
