Malolactic Fermentation (MLF)

Malolactic fermentation (MLF) meaning in wine

Malolactic fermentation is a secondary bacterial conversion process that occurs after alcoholic fermentation, transforming sharp malic acid into softer lactic acid. Despite its name, MLF is not technically a fermentation but rather a decarboxylation process carried out primarily by Oenococcus oeni bacteria. This naturally occurring or induced process converts approximately 6-7 grams per liter of malic acid into lactic acid, simultaneously producing carbon dioxide and diacetyl, a compound responsible for the characteristic buttery aroma and mouthfeel. MLF typically occurs at temperatures between 18-22°C and can take several weeks to months to complete. Nearly all red wines undergo malolactic fermentation to soften their acidity and enhance complexity, while select white wines like Chardonnay and Viognier may also undergo partial or complete MLF to achieve a creamier texture and richer mouthfeel. The process reduces wine acidity by approximately 1-3 g/L, creating a smoother, more rounded palate. Winemakers can encourage MLF through inoculation with commercial bacteria strains or prevent it using sulfur dioxide additions. The timing and extent of malolactic fermentation significantly influences a wine’s final flavor profile, texture, and aging potential.