Enhancing Vin Santo Quality Using a Saccharomyces cerevisiae/Zygosaccharomyces rouxii Mixed Starter Culture

The principal critical issue in the production of Vin Santo passito wine is the high likelihood of fermentation arrests or sluggish fermentation, resulting in low sensory quality. A potential solution is to select indigenous yeasts from well-conducted spontaneous fermentations. In this study, a novel mixed starter culture consisting of two indigenous strains, Saccharomyces cerevisiae Ris III and Zygosaccharomyces rouxii Zr186, was evaluated. After selecting the strains and testing their compatibility, the mixed culture was used as a starter in the winemaking process of dried grapes, which was conducted in barrels of various sizes. The fermentations were monitored microbiologically for a period of 100 days to verify the ability of the inoculated strains to dominate and thus facilitate the fermentation process. Both strains dominated the fermentations: S. cerevisiae showed a 100% isolation rate immediately, while Z. rouxii achieved dominance within a month. The mixed starter demonstrated a 25% improvement in fermentation purity for the same barrel size. Sensory analyses revealed that the wines produced with the mixed starter were very consistent with one another, contrasting with those obtained through spontaneous fermentations, and received the highest scores for gustatory descriptors. In conclusion, this mixed culture represents an effective strategy for standardizing fermentation and improving the sensory quality of Vin Santo.