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.
