## 3 Results and Discussion
### Cell Growth Dynamics of the Strains and Evolution of Total Soluble Solids during Mixed Fermentation
zenplinina_, occurred very slowly; in fact, the reduction of TSS until 5 \({}^{\circ}\)P required 10 days in PW fermentation, whereas more time was necessary in the WW and AW fermentations. The cell dynamics during the process are an important parameter in fermentation. In brewing practice, the yeast biomass collected after fermentation is used as the inoculum for subsequent batch fermentations. Therefore, keeping yeast cell viability as high as possible is a desired trait for the brewing process. Moreover, cell viability has an impact on the fermentation kinetics and beer quality [40]. Usually, the number of viable cells diminishes substantially during beer fermentation inoculated with _S. cerevisiae_[41]. In our study, the _S. cerevisiae_ P4 strain in single fermentation showed similar pattern in all the words during the first 6-10 days of the process, with an increase in cell numbers in the first 3 days. Subsequently, the number of viable cells remained constant in Pilsner fermentation, whereas a decrease was observed in the other two words, particularly in Amber production, where the cell number significantly decreased at the end of the process. In the mixed fermentations, different trends were recorded in the function of the non-_Saccharomyces_ strain included in the starters. In the fermentation by mixed culture P4-CR1, the non-_Saccharomyces_ strain (_Z. bailii_) maintained similar cell viability during Pilsner production, whereas a high decrease in cell viability during the process was observed for the P4 strain. For the fermentations performed in WW and AW, the CRI strain underwent a decrease (from 9.35 \(\times\) 10\({}^{6}\) to 3.50 \(\times\) 10\({}^{6}\) and from 9.50 \(\times\) 10\({}^{6}\) to 2.15 \(\times\) 10\({}^{6}\), respectively), whereas the P4 strain showed similar cell viability to single fermentation. These results might indicate a competition between _S. cerevisiae_ and non-_Saccharomyces_ strains, as the prevalence of the non-_Saccharomyces_ strain over _S. cerevisiae_ was observed when the cell numbers of the _S. cerevisiae_ strain were lower than non-_Saccharomyces_ cells, such as in Pilsner fermentation. A different result was detected in the fermentation by the mixed culture P4-LC2-1, where the two strains (_S. cerevisiae_ and non-_Saccharomyces_) exhibited similar trends in Pilsner and Amber productions, with the viable cells of the non-_Saccharomyces_ strain (_T. delbrueckii_) were very similar to the cell numbers of P4, i.e., 1.30 \(\times\) 10\({}^{6}\) and 1.85 \(\times\) 10\({}^{6}\), respectively, in Pilsner, and 2.85 \(\times\) 10\({}^{6}\) (LC2-1) and 4.95 \(\times\) 10\({}^{6}\) (P4) in Amber fermentation. In the WW, a similar trend between the two strains was observed in the first few days, while after the sixth day, the cell numbers of the _S. cerevisiae_ strain (P4) were higher (1.70 \(\times\) 10\({}^{7}\)) than those of LC2-1 (2.40 \(\times\) 10\({}^{6}\)). This result was very similar to data obtained in WW fermentation with the P4-CR1 mixed starter. The two mixed cultures with _C. zenplinina_ as a non-_Saccharomyces_ yeast (P4-TSF and P4-CZ3) showed a similar trend of cell numbers in each word, whereas differences in the evolution of cell number were found as a function of the word used. In PW, both TSFand CZ3 showed a decrease in cell numbers after the third fermentation day, with high reduction during bottle refermentation (after the 10 th day), reaching 5.40 \(\times\) 10\({}^{4}\) (TSF) and 2.35 \(\times\) 10\({}^{4}\) (CZ3) cells/mL. In WW fermentation, similar trends for the evolution of _C. zemplinina_ cells were found in the first step, after primary fermentation (until the 10 th day), for both the strains, whereas in the last step, the number of viable cells was higher than the levels detected in PW fermentation (1.05 \(\times\) 10\({}^{6}\) for TSF and 5.55 \(\times\) 10\({}^{5}\) for CZ3). For brewing performed in AW, a rapid decrease in _C.