Malolactic Fermentation

Malolactic fermentation, also called malolactic conversion, is a winemaking process in which tart tasting malic acid, naturally present in grape must, is converted into softer tasting lactic acid. It is most often carried out as a secondary fermentation shortly after the primary fermentation ends, though it can sometimes run alongside it, and it is standard practice for most red wine production and common for some white varieties such as Chardonnay, where it can lend a buttery flavor from a byproduct called diacetyl. The reaction is carried out by lactic acid bacteria, chiefly Oenococcus oeni along with various Lactobacillus and Pediococcus species, and chemically it is a decarboxylation that releases carbon dioxide.