Pilot-scale assessment of native Uruguayan yeast strains for Tannat wine fermentation

In recent decades, there has been renewed interest in studying and utilising indigenous yeast strains to preserve the unique characteristics of the terroir, thus producing wines that truly reflect their place of origin. A key challenge is the identification of non-conventional yeasts capable of both completing fermentation and enhancing a wine's uniqueness, complexity, and sensory appeal. In this study, we evaluated the oenological potential of three selected native strains, Saccharomyces cerevisiae 3FS, Saturnispora diversa 1FS, and Starmerella bacillaris 3MS, through pilot-scale fermentations of Tannat must in 200-L stainless steel tanks. We also explored the influence of these strains on the volatile compound profiles of the resulting wines. The native strains exhibited notable kinetic fermentative similarities to the reference strain S. cerevisiae RX60, thus demonstrating their comparable robust fermentative power, which is crucial for ensuring reliable fermentation in a commercial setting. This confirms that these strains can independently conduct fermentation. All three native strains consumed approximately 99 % of the must sugars within 11 days of alcoholic fermentation, achieving ethanol concentrations in the range of 9.65–11.58 %. Pilot-scale trials highlighted the pronounced fructophilic nature of S. bacillaris 3MS, which left very low levels of residual fructose (0.06 ± 0.05 L-1). This strain fermented glucose at a significantly lower rate than it did fructose, resulting in a final glucose-to-fructose (G/F) ratio of 1.83, which is considerably higher than that observed for the other strains (0.41–0.50). Moreover, fermentation with S. bacillaris 3MS reduced ethanol content by 2 % (v/v) compared to the Saccharomyces cerevisiae strains; such behaviour is advantageous for producing wines with lower alcohol levels. Fermentations using native strains produced wines with more pronounced floral and fruity aromas: specifically, S. bacillaris 3MS significantly increased the total concentrations of volatile esters, norisoprenoids, and terpenes, as detected by GC-MS, relative to the other species. The approach used here can enable winemakers to utilise non-Saccharomyces yeasts, such as S. bacillaris 3MS and S. diversa 1FS, to enhance wine aroma, while promoting biodiversity, fostering innovation, and creating wines with greater authenticity and uniqueness.