Potential of native Uruguayan yeast strains for production of Tannat wine

Abstract

Must fermentation is a complex process influenced by various factors, especially microbiological activities. The characteristics and quality of the resulting wine are closely linked to the stages that unfold throughout this progression. Winemakers usually use pure cultures like Saccharomyces cerevisiae to ensure a reliable and complete process. Alternatively, the use of commercial wine yeasts is somewhat controversial, as it may lack certain desirable characteristics provided by natural fermentation. A key challenge is finding non-conventional yeasts that complete fermentation while enhancing a wine’s uniqueness, complexity, and appeal. In our previous studies, we isolated, identified, and conducted physiological and biochemical characterizations of indigenous yeasts from Tannat grapes in the Maldonado vineyard (1). Three strains demonstrated notable fermentation properties: Saccharomyces cerevisiae T193FS, Saturnispora diversa T191FS, and Starmerella bacillaris T193MS. In this study, we assessed the oenological potential of these strains at a semi-pilot scale during the vinification of a Tannat must with an expected ethanol content of 11-12%. All three native strains consumed around 98% of the must sugars, resulting in robust ethanol production in the range of 9-11%. Pilot-scale trials highlighted the strong fructophilic character of S. bacillaris, which left very low residual fructose levels (0.006 g/L compared to ≥0.01 g/L for the other species) while yielding lower ethanol (9%), a profile beneficial for crafting lower-alcohol wines.

Wines with native strains, stood out for presenting greater fruity notes, especially S. bacillaris, showed enhanced fruity notes like plum, raisins, and candied fruit, linked to higher ester, norisoprenoid, and terpene levels detected by GC-MS. The β-glucosidase activity of these strains was also investigated, as this enzyme enhances aromatic complexity by releasing aroma compounds from glycosidic precursors during fermentation. Given its notably high β-glucosidase activity under acidic conditions of S. diversa T191FS, it was subsequently evaluated as a pure starter in Muscat wine fermentation. Volatile compound analysis by GC-MS showed a significant increase in total terpenes compared to the commercial strain S. cerevisiae (145 vs. 45 ug/L, respectively). S. diversa stood out for its ability to release terpenic varietal aromas.

References

[1] Morera G, de Ovalle S, González-Pombo P. Prospection of indigenous yeasts from Uruguayan Tannat vineyards for oenological applications. Int Microbiol. 2022 Nov;25(4):733-744. doi: 10.1007/s10123-022-00257-6. Epub 2022 Jun 21. PMID: 35727473.