🍷 Malic acid

Malic acid is one of the two main organic acids of grapes, along with tartaric acid. It builds up in the berry until veraison, when it is the major organic acid (up to 25 g/L), and then falls steadily during ripening to roughly 1 to 5 g/L at maturity. Other acids, such as citric acid, make up only a small fraction of the acids in grape juice.

Warm conditions speed up the breakdown of malic acid, so grapes grown in cool climates tend to keep more of it at harvest. Tartaric acid is more stable than malic acid.

In malolactic fermentation, lactic acid bacteria, most often Oenococcus oeni, decarboxylate L-malic acid to L-lactic acid. This decreases the acidity of the wine, changes its chemical and sensory characteristics and increases its biological stability. The majority of red wines and some white wines are produced using it.