Fermentation kinetics of Pichia kluyveri-Saccharomyces cerevisiae in Nebbiolo must.

The beneficial role of mixed-culture fermentations involving Saccharomyces cerevisiae and non-Saccharomyces yeasts in winemaking is well established. It is consistently observed that non-Saccharomyces species are rapidly outcompeted and decline in viability when co-inoculated with S. cerevisiae. However, the extent and dynamics of this phenomenon are known to be species and strain dependent. Despite these findings, only a limited number of studies have focused on mixed fermentations involving Pichia kluyveri strains. In this study, four strains of P. kluyveri and two strains of S. cerevisiae were evaluated under different fermentation conditions to investigate strain-specific interactions, viability trends and their impact on main enological metabolites. Individual population kinetics were analyzed using the Baranyi growth model. Chemical analyses revealed significant differences in acetic acid production and in ethanol and glycerol yields among wines, in a strain-dependent way. These differences could be explained by the growth dynamics of the two species during fermentation. Notably, all P. kluyveri strains exhibited a faster decline in mixed fermentations compared to pure cultures, regardless of the inoculation strategy (simultaneous or sequential). The observed reduction in viability could be partially linked to metabolites produced during fermentation.