In the malolactic fermentation, which is the second wine fermentat ion, the malic acid is consumed by lactic acid bacteria to yield lactic acid, resulting in a reduction of the wine fixed acidity. This fermentation can begin during the alcoholic fermentation or after its completion. It must be controlled for improving the organoleptic characteristics and the microbiological stability of wines. If uncontrolled, several unpleasant substances may be formed originating loss of quality of the wine.