Malolactic fermentation

Malolactic fermentation (or sometimes malolactic conversion or MLF) is a process in winemaking where tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid. Malolactic fermentation tends to create a rounder, fuller mouthfeel. It has been said that malic acid tastes of green apples. By contrast, lactic acid is richer and more buttery tasting. Grapes produced in cool regions tend to be high in acidity much of which comes from the contribution of malic acid. MLF is also thought to generally enhance the body and flavor persistence of wine, producing wines of greater palate softness and roundness. Many winemakers also feel that better integration of fruit and oak character can be achieved if MLF occurs during the time the wine is in barrel.

Use in winemaking

MLF usually occurs shortly after the end of the primary fermentation. It is undertaken by the family of lactic acid bacteria (LAB); Oenococcus oeni, and various species of Lactobacillus and Pediococcus. The primary function of all these bacteria is to convert one of the two major grape acids found in wine called L- malic acid, to another type of acid, L+lactic acid. The onset of MLF in the bottle is disastrous as the wine will appear to the consumer to still be fermenting (as a result of CO₂ being produced). The wine may also lose its fruit integrity and take on the unpleasant lactic aroma of cured meats.

Process

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 tarter, more acidic profile in the finished wine.^[1] Chemically, malolactic fermentation is a decarboxylation, which means that 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.

References

1. ^ http://www.vicivino.com/AskTheWinemakerArchive.aspx?id=0

External links

• Purdue University - "The Joy of Malolactic Fermentation" Accessed Dec. 27th, 2007