Malolactic fermentation

Sometimes shortened as MLF, this is a bacterial fermentation which can occur after yeast fermentation winds down or finishes. The bacterium Bacillus gracile converts malic acid into lactic acid and carbon dioxide. Lactic_acid is much less harsh than malic and thereby softens and smooths the wine, but the wine also is endowed with a cleaner, fresher taste. In addition, diacetyl (or biacetyl) is produced as a byproduct, which resembles the smell of heated butter and adds complexity to wine. MLF is a positive event in some cases and has a downside in others - the fruitiness of wines undergoing MLF is diminished and sometimes off odors can result. To ensure MLF, the wine should not be heavily sulfited and it should be inoculated with an MLF culture.