Malic acid is a naturally occurring organic acid found in grapes and many fruits, especially green apples. It contributes a sharp, tart sensation to grape must and wine. The amount of malic acid in grapes generally decreases as they ripen, and it can be converted into lactic acid during malolactic fermentation.
Malic acid is one of the principal acids in grape juice, along with tartaric acid. Cooler growing conditions often help grapes retain more malic acid, while warm temperatures during ripening can accelerate its loss. Variety, vineyard site, harvest timing and vintage also influence the final concentration.
During malolactic fermentation, lactic acid bacteria convert malic acid into lactic acid and carbon dioxide. This reduces the wine’s total acidity and usually softens its sensory profile. Winemakers may encourage MLF for most red wines and selected whites, or prevent it when they want to preserve a crisp, high-acid style.
Malic acid contributes a tart, green-apple impression. Lactic acid is generally perceived as softer and rounder. The actual sensation depends on pH, total acidity, residual sugar, alcohol and other wine components.
Example: a cool-climate Riesling may retain noticeable malic acidity and show crisp apple and citrus character, while a Chardonnay that has undergone MLF may have a softer acid profile.
Malic acid can be metabolised by lactic acid bacteria during MLF. Tartaric acid is more stable in wine and may form potassium bitartrate crystals during cold storage. Both contribute to total acidity but behave differently during winemaking.
Chef’s note: malic acidity can make a wine feel crisp and refreshing. Consider it when pairing with rich food, but assess the wine’s overall balance rather than relying on one acid descriptor.
This term is one of hundreds covered in depth across OCS courses, learning paths, and 1-on-1 coaching with Chef Eric.
