Science of Wine

Our ever-expanding list of Wine Science terms.



The abbreviation of alcohol by volume, listed by percent on a wine label (e.g., 13.5% ABV).


A toxic organic chemical compound that is produced in our bodies in order to metabolize ethyl alcohol. The cause of alcohol poisoning.

Amino Acids

Organic compounds; the building blocks of proteins. Red wine contains 300–1300 mg/L of amino acids, of which proline accounts for up to 85%.

Aroma Compounds

Chemical compounds with very low molecular weights, making it possible for them to be carried into the upper nasal passage. Aroma compounds are derived from grapes and fermentation and are volatilized by the evaporation of alcohol.



An organic compound found in wine that tastes like butter. Diacetyl comes from oak aging and malolactic fermentation.



Esters are one type of aroma compound found in wine, which are caused by alcohol reacting with acids in wine.



A colorless, odorless, viscous, sweet-tasting liquid that is a byproduct of fermentation. In red wines there are about 4–10 g/L and noble rot wines contain 20+ g/L. Glycerol has been considered to add a positive, rich, oily mouthfeel to wine, however, studies have shown that other traits, like alcohol level and residual sugar, have a greater effect on mouthfeel.



A figure that expresses the acidity or alkalinity in a substance numbered from 1–14, where 1 is acid, 14 is alkaline, and 7 is neutral. Wine’s average range is about 2.5–4.5 pH and a wine with a pH of 3 is ten times more acidic than a wine with a pH of 4.


A group of several hundred chemical compounds found in wine that affect the taste, color, and mouthfeel of wine. Tannin is a type of phenol called a polyphenol.


Residual Sugar (RS)

The sugar from grapes left over in a wine after a fermentation stops. Some wines are fermented completely dry, and some are stopped before all the sugar is converted to alcohol to create a sweet wine. Residual Sugar ranges from nothing to upward of 400 grams per liter for very sweet wines.



Sulfites, sulfur dioxide, or SO2 is a preservative that is either added to wine or present on grapes before fermentation. Wines range from about 10 ppm (parts per million) to 350ppm—the legal US limit. Wines must label if they contain more than 10 ppm.

Sulfur Compounds

Sulfur compounds affect the aroma and taste of wine. In low levels they offer positive aroma characteristics, including mineral-like flavors, grapefruit, or tropical fruit. In higher levels, sulfur compounds are considered a fault when they smell of cooked eggs, garlic, or boiled cabbage.



The primary extract of the vanilla bean, also found in toasted oak barrels.

Volatile Acidity (VA)

Acetic acid is the volatile acid in wine that turns wine to vinegar. In small levels it adds to the complexity of flavor and in high levels it causes the wine to spoil.

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