Transformation of malic acid into lactic acid under the action of malolactic bacteria. Malolactic fermentation (or MLF) leads to a decrease in acidity and an increase in the suppleness of the wine. It stabilizes the wine microbiologically.
Malolactic fermentation has only been known since the middle of the 20th century. In the past, winemakers often observed the wine being “reworked” in the spring. If this step had not occurred spontaneously, the wine could “rework” in the bottle. The result was not very convincing from a gustative point of view…
In practice, today, a good winemaker must master “la malo”. Malolactic bacteria are naturally present in wine. Once the alcoholic fermentation is over, maintaining the temperature at around 23-24°C favours the start of MLF after a few days to a few weeks. It is possible, if one wishes to shorten the latency period, to use bacteria selected and multiplied in the laboratory.
MLF is mandatory for Bordeaux red wines, optional, and even generally undesirable for whites and rosés.
For more information, a blog article : La fermentation malolactique stabilise le vin nouveau