Yeasts are microorganisms which are responsibe for the fermentation of sugar into alcohol. Nearly 1000 different types of yeast were used today. About 2,2% of yeast were added to the mash and the yeast double in about two hours. There are violent reactions in the washback and the temperature increases steadily. The wash starts to foam and rotation knives cut the foam to hold it under control. Sometimes the yeast will be took out from the washback for the next fermentation or the yeast can also be cultured in the laboratory. Yeast is available in dry form and is added to the mash powdery or in a solution. The yeast need no other enzyme or other substances for the fermentation. Mixtures of yeasts are used very often. The more complex the mixture is the more complex is the alcohol you will get. Brewers yeast maximises the taste and the aromas, cultivated yeast maximises the alcohol. Some distilleries uses only one to four different yeasts, others have their own yeast cocktails. Yeast produces not only alcohol, there will also be ester, aldehydes, acids and higher alcohols which are very important for the differences in taste and aroma.