Weinsäure

Weinsäure, known in English as tartaric acid, is a naturally occurring dicarboxylic acid widely found in grapes and wine. Its molecular formula is C4H6O6 and its structure is HOOC-CHOH-CHOH-COOH, giving it two carboxyl groups and two adjacent hydroxyl-bearing carbon atoms.

Chemistry and stereochemistry: Tartaric acid contains two stereocenters, which leads to three stereoisomers: two enantiomers (the D- and L- forms) and a meso form. This stereochemical diversity underpins its behavior in biological systems and its distinction in various natural sources.

Occurrence and relation to wine: It is a major organic acid in grapes and contributes to the characteristic tartness of grapes and wine. In wine, tartaric acid forms salts with potassium or calcium, notably potassium bitartrate (cream of tartar), which can crystallize as tartrate crystals in bottles or casks, commonly referred to as wine diamonds.

Properties: Tartartic acid is a weak diprotic acid. Its pKa values are typically around 3.0 for the first dissociation and about 4.3 for the second. It is highly soluble in water and forms esters and salts readily.

Applications and uses: In the food and beverage industry, tartaric acid is used as an acidity regulator (listed as E334). It also serves in baking and confectionery, where potassium bitartrate (cream of tartar) is used to stabilize foams and as a leavening agent when combined with baking soda. Tartrate salts find various roles in winemaking and food processing, while the acid itself is a common additive due to its flavor and buffering properties.