In the industrial beer production yeast repitching is often used to decrease economic cost of production, this can lead to genetic modifications in the yeast cells. The aim of the master thesis was to characterize the genetic stability of chosen strain isolated from Carinthian cider Saccharomyces cerevisiae ZIM 3704, during 30 series of one-week fermentations of barley, buckwheat and millet wort in conical minifermentors at 14 °C. During each week we determinated cell viability with cultivation on a solid medium and method of methylene blue staining, we also determinated flocculation rate. Cell viability results were dependent upon among different types of worth (buckweat, barley and millet), but after 30 uses they are still around 95%. Flocculation analysis showed that the strain used for fermentation of barley wort had the highest flocculation, while the strain used for fermentation of millet wort had lowest. With HPLC analysis we determinated strain capability of sugar uptake in different worths and primary metabolite production. We showed that maltose uptake is higher at 30th fermentation then at the first one. The consumed maltotriose increased with increasing consumption of maltose. Concentration of ethanol and glycerol were inversely proportional connected, because when the concentration of glycerol gets higher, the concentration of ethanol falls. In addition, it was also determinated genetic stability between different yeast morpotypes after 30. repitches in DNA microsatellite region and lenght changes in chromosome with pulse-field electrophoresis. Both methodes showed no changes, so we proved them with next generation sequencing, which showed presence of new retrotransposones and noncoding regions among exons
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