Malolactic fermentation refers to the development of lactic bacteria mainly belonging to the genera Oenococcus, Lactobacillus, Pediococcus and Leuconostoc.
During this fermentation, malic acid is broken down into lactic acid. This change from a diacid to a monoacid results in a decrease in acidity. Since malic acid can be used by spoilage microorganisms, its disappearance leads to an increase in the wine's microbiological stability.