“Malolactic fermentation” characterizes fermentation by bacteria that are able to convert malic acid from grapes into lactic acid. It occurs together with the regular alchololic fermentation. It reduces the bitter tasting malic acid to the softer lactic acid and add ‘buttery’ flavor to the wine.
Wines made from concentrate are generally inappropriate for malolactic treatment due to the low solid and low acidity levels. In general high quality wines made from grapes get malolactic treatment.
The same bacteria responsible for production of lactic acid is also responsible for the production of acetic acid which is the acid that gives typical vinegar flavor.Therefore, uncontrolled malolactic fermentation is unacceptable.
Malolactic bacteria are not remarkably alcohol tolerant and a wine with alcohol level higher than 14% will not support it.
Because malolactic fermentation can cause the pH of the wine to rise, it may make it susceptible to other bacterial infections. Therefore sulphite levels needs to be adjusted.
If the wine is kept at relatively warm temperatures the fermentation will be complete within two months. If you wish to know that malolactic fermentation is complete, an accurate chromatography test is the only way to find out.