Malolactic fermentation takes place generally in red wines after alcoholic fermentation and consists on the change from malic acid (mainly present in the pulp of the grape), into lactic acid by means of naturally bacteria found in the skin grape and therefore also in the newly fermented wine.
Malic acid is one of the responsible for the marked acidity and freshness that we find in white wines, so in this type of elaborations it is not necessary to do this process, although there are some exceptions. In the elaboration of red wines it is usual to favor the transformation of this acid, mainly to reduce the acidity and to give a more pleasant and voluminous sensation in the mouth, thus achieving the softness in the wine.
The time that takes this fermentation also depends on several factors like the temperature and the quantity of malic acid existing in the wine, but it usually takes from two weeks to several months. This process can be done in stainless steel tanks or directly in oak barrels, and must be strictly controlled by wine makers.