Acids in Wine - Tartaric Acid

Tartaric Acid

Tartaric acid is, from a winemaking perspective, the most important in wine due to the prominent role it plays in maintaining the chemical stability of the wine and its color and finally in influencing the taste of the finished wine. In most plants, this organic acid is rare, but it is found in significant concentrations in grape vines. Along with malic acid, and to a lesser extent citric acid, tartaric is one of the fixed acids found in wine grapes. The concentration varies depending on grape variety and the soil content of the vineyard. Some varieties, such as Palomino, are naturally deposed to having high levels of tartaric acids, while Malbec and Pinot noir generally have lower levels. During flowering, high levels of tartaric acid are concentrated in the grape flowers and then young berries. As the vine progresses through ripening, tartaric does not get metabolized through respiration like malic acid, so the levels of tartaric acid in the grape vines remain relatively consistent throughout the ripening process.

Less than half of the tartaric acid found in grapes is free standing, with the majority of the concentration present as potassium acid salt. During fermentation, these tartrates bind with the lees, pulp debris and precipitated tannins and pigments. While some variance among grape varieties and wine regions exists, generally about half of the deposits are soluble in the alcoholic mixture of wine. The crystallization of these tartrates can happen at unpredictable times, and in a wine bottle may appear like broken glass, though they are in fact harmless. Winemakers will often put the wine through cold stabilization, where it is exposed temperatures below freezing to encourage the tartrates to crystallize and precipitate out of the wine.