The yeast activity is the focal point of the fermentation process and converts the nutrients in the dough during the fermentation time. The yeast cells take the dissolved nutrients into the inside of the cells, while the enzymes in the cells ferment the sugar substances (mono- and disaccharides). The formation of the aeration gas carbon dioxide is the primary aim of the yeast fermentation. Over and above, alcohol is also always formed, the reason why the yeast fermentation is also called alcoholic fermentation. The alcohol evaporates completely during baking and is no longer contained in the baked goods.
The enzymes contained in the yeast cells and the corresponding metabolic products are shown in table 5.19.
Table 5.19: Examples of yeast enzymes and their effect on sugar substances
Due to the aeration gas carbon dioxide, the dough pieces are given a larger volume and the dough matrix is structured during the fermentation process. Over and above, besides the fermentation process, other maturing processes take place in the dough piece. During the fermentation phase, dough swelling also increases, whereby a better stability of the dough pieces is obtained.