The principal organic acids found in grapes are tartaric, malic, and to a small extent, citric. Many other organic acids, including amino acids, are also found in juice and wines, but tartaric and malic acid account for over 90% of the total acids present. During the early period of berry growth, concentration of both acids increases in the fruit. With the onset of ripening, as the sugar accumulates in the fruit, the acid concentration decreases. Generally the reduction in malic acid is greater, and consequently, at maturity, the fruit contains more tartaric acid than malic.
- Grapes are one of the rare fruits that contain tartaric acid. It is present as free acid and a salt, such as potassium bitartrate. Bitartrate is an important constituent since it affects pH and the cold stability of the wine. The acid composition of grapes is influenced by many factors such as variety, climatic region, and cultural practices.