As the second fermentation of wine, it is not a necessity but more a preference in which winemakers favour a softer and more rounded mouthfeel. Used primarily in the red wine process, yet most noticeable in Chardonnay wines, the region of Chablis in Burgundy is the primary French region to perform malolactic fermentation.
This step in the vinification process can occur during primary (alcoholic) fermentation but often occurs later, after the must has been settled. Commencing with the addition of malic acid bacteria culture (Oenococcus oeni), the existing malic acid is converted to lactic acid. The production of carbon dioxide bubbles bursting at the surface is a key sign the fermentation is underway, with winemakers keeping a close eye on the entire process. Once the desired level has been reached, winemakers can stop the process before all malic acid is converted by adding in sulphur dioxide to kill the bacteria, or adding an enzyme that inhibits the malolactic process.
As malic acid presents a tart and harsh flavour profile, lactic acid is a lot softer and ‘buttery’ in taste. This process can also intensify fruit flavours in red wines and lower the harsh tannins at the same time. Both acids have elements winemakers may favour and so a final blending can be done to create a wine blend of juice that has and has not gone through malolactic fermentation.
As an added benefit, the winemakers have more certainty in their bottled wines that malolactic fermentation won’t be triggered in bottle and is a more stable product to be held in cellar.