Once the sugar is converted into alcohol, and the alcoholic fermentation is completed, begins a process called malolactic fermentation, where lactic acid bacteria convert the malic acid to lactic acid; and thus contribute to the finished product.
The temperature plays a very important role. In warmer climates, this process takes place spontaneously, when temperatures rise; in the colder regions, however, the malolactic fermentation has to be initiated.
One of the advantages of this second fermentation is that the development of toxins or other harmful organisms, such as bacteria, is avoided, and thus a longer preservation of the beverage can be achieved. The red wines, which are run through this process, have a lower acidity, the color is less intense, and the fragrance is complex and sophisticated. On the nose and on the palate the existing lactic acid raises notes of milk, yogurt or butter, and the wine gets supple and balanced.