The fermentation process is the base of the creation of wine. At this stage the wine producers usually intervene with destruction of wild and unpredictable natural yeasts, introducing yeast type of their choice, with which they achieve control of the fermentation process and get wine with the desirable properties. Once the process of fermentation starts, it lasts until the full sugar content of the must is not transformed into alcohol. The entire process can take from 10 days to a month or more. The final content of alcohol in the wine varies with different wines and depends on the total amount of sugar in the grapes, as well as on the climate in which the grapes are grown (10% alcohol in the colder regions and 15% alcohol in the warmer regions are considered as optimal values). Sweet wines are produced when the fermentation process is terminated before the full amount of sugar is transformed into alcohol. Besides alcohol, the so called malolactic fermentation is also present in the wines. This fermentation represents the conversion of the malic acid into lactic acid and has a big impact on the taste of the wine.