Chemical composition of wine has been the topic of research since decades as it is a popular alcoholic beverage with supposedly beneficial effects on human health. Water and alcohol are the major ingredients in most wines while minute quantities of various other components are also present. Winemakers add certain other substances to lend a distinct character, quality, flavor, and taste to the wine. Composition of wine can be broadly classified into two categories – volatile and fixed.
Water: It is derived from grape juice and forms about 85 percent of wine.
Alcohol: It constitutes approximately five to fifteen percent of wine and is responsible for its redolence. It is formed by conversion of sugars with yeast. Ethyl alcohol is the main alcohol in quantity. Glycerol, butylene glycol, and other poly and cyclic alcohols are present. Alcohol obtained by distillation is added to fortified wines.
Acids: They form about one percent of wine. Tartaric acid is the major acid that is derived from grapes. In combination with organic acids like malic and citric acid they add to the flavor of wine. Volatile acids like acetic, succinic, lactic, and oenanthic acid are produced during fermentation.
Sugars: Sweet wines have about ten percent sugar content while dry wines have only about 0.1 percent. These along with alcohols and other substances are responsible for the sweetness of wine.
Mineral Salts: They form about 0.2 to 0.4 percent of wine and account for its freshness and flavor. Common mineral salts that are found are sodium, potassium, magnesium, calcium, and iron.
Sulfites: Upper limit for Italian wines is 200 parts per million. Sulfites are used to sterilize and preserve wines.
Phenols: Phenols form about 0.01 to 0.5 percent of wine. Phenolic compounds like anthocyanins and tannins impart color to the wine and are also responsible for differences in flavor.
In addition to the above traces of aldehydes, ketones, and esters are also found in wines.