The Composition of Wine

Wine is defined for legal purposes as "a water and alcohol solution obtained from the complete or partial fermentation of fresh grapes or grape must." The basic ingredients of wine are water and alcohol, though other components present in miniscule quantities have a determining effect on quality and character. Wine consists of:

Water (80%-85%
The hydrogen dioxide in wine derives from grape juice so it is biologically pure. It is the essential base for all of the complex bio-chemical phenomena that occur as the wine is made and aged.

Alcohols (10%-20%)
Alcohol in wine is produced by sugar-converting yeasts. The most important alcohol in quantity terms is ethyl, a monoalcohol, followed by glycerol, a polyvalent alcohol that adds a degree of sweetness and finally by higher alcohols such as proponol, butanol and isoamyl.

Acids (0.4%-1%)
Three organic acids, tartaric, malic and citric are natural components of grapes. The three others present in wine, succinic, lactic and acetic acid (the source of volatile acidity) are produced by fermentation.

Sugars
The glucose and fructose contained in grapes is mainly converted into alcohol through fermentation. The sugar left in the completed wine varies from around 0.1% (1 g/l) for dry wines to 10% (100 g/l) in sweet wines.

Mineral salts (0.2%-0.4%)
Salts derived from minerals and organic acids lend freshness to the flavor of wine. The most important are potassium, sodium, magnesium, calcium and iron.

Coloring substances (0.01 %-0.5 %)
Phenolic pigments known as leuco-anthocyanins are present in white wines. The color of red wines derives from polyphenols in the form of anthocyanins and tannins contained in grape skins.

Aromatic substances (0.01%-0.1%)
Traces of various chemical compounds contribute to the aroma of a wine. These volatile substances include alcohols, aldehydes, esters, acids and ketones.

Sulfites
Sulfur derivatives are used to safeguard grapes and sterilize and preserve wines. The presence of sulphites at 10 to 200 parts per million is measured both in fixed sulphur dioxide, combined with other substances in the form of gas.