In winemaking, malolactic fermentation (MLF) converts malic acid to lactic acid, with CO2 being the byproduct of the reaction. MLF, which is typically carried out in most red wines and in some white varietals, plays an important role in the finished wine’s feel and taste. MLF reduces titratable acidity, increases pH, and produces flavors often characterized as “soft” or “buttery”.
Sulfite, as free SO2, inhibits the bacteria that carry out MLF. Therefore free SO2 levels must be kept low during MLF, carrying risks that the wine is left unprotected against oxidation and microbial contamination. As soon as MLF is done, then, SO2 should be raised to appropriate levels for protection of the wine. Thus it is important to know when MLF is done, and the best way to do this is to measure malic acid levels in the wine.