Page "Malolactic fermentation" Paragraph 2

Malolactic conversion is accomplished by lactic acid bacteria ( such as Oenococcus oeni ), which consume malic acid to liberate energy.

This can occur naturally.

However, in commercial winemaking, malolactic conversion typically is initiated by an inoculation of desirable bacteria.

This prevents undesirable bacterial strains from producing off flavors.

Conversely, commercial winemakers actively prevent malolactic conversion when it is not desired, to prevent accidental initiation and maintain a more tart or acidic profile in the finished wine.

Chemically, malolactic fermentation is a decarboxylation, which means carbon dioxide is liberated in the process.

Because it consumes malic acid, which is present at the time the grapes are crushed, malolactic conversion can take place at any time during or after alcoholic fermentation.

A wine undergoing malolactic conversion will be cloudy due to the presence of bacteria, and may have the curious smell of buttered popcorn, due to the production of diacetyl.