Abstract
Each wine growing region hosts unique communities of indigenous yeast species, which may enter fermentation and contribute to the final flavour profile of wines. One of these species, Saccharomyces uvarum, is typically described as a cryotolerant yeast that produces relatively high levels of glycerol and rose-scented volatile compounds as compared with Saccharomyces cerevisiae, the main yeast in winemaking. Comparisons of fermentative and chemical properties between S. uvarum and S. cerevisiae at the species level are relatively common; however, a paucity of information has been collected on the potential variability present among S. uvarum strains. The objective of this study was to compare the fermentation kinetics and production of volatile compounds between indigenous and commercial Saccharomyces strains at different temperatures. We compared laboratory-scale fermentation of Chardonnay juice at 15 °C and 25 °C for 11 Saccharomyces yeast strains (six indigenous S. uvarum, one commercial S. uvarum, one indigenous S. cerevisiae and three commercial S. cerevisiae). Fermentation kinetics and the production of volatile compounds known to affect the organoleptic properties of wine were determined. The indigenous S. uvarum strains showed comparable kinetics to commercially sourced strains at both temperatures. Volatile compound production among the strains was more variable at 15 °C and resulted in unique chemical profiles at 15 °C as compared with 25 °C. Indigenous S. uvarum strains produced relatively high levels of 2-phenylethyl acetate and 2-phenylethanol, whereas these compounds were found at much lower levels in fermentations conducted by commercial strains of both S. cerevisiae and S. uvarum. Production of glycerol by indigenous S. uvarum strains did not differ from commercial strains in this study. Our findings demonstrate that indigenous strains of S. uvarum show functional variation among themselves. However, when compared with commercial S. cerevisiae and S. uvarum strains, they have comparable fermentation kinetics but unique volatile compound profiles, especially at low fermentation temperatures.
Highlights
While many factors affect the final aromas and flavours of wine, including grape varietal, available sugars, assimilable nitrogen, pH and fermentation temperature, different yeast strains can impact wine quality by producing different concentrations of volatile compounds (Fleet, 2003; Romano et al, 2003)
All strains conducted alcoholic fermentation more slowly at 15 °C than at 25 °C and most S. uvarum strains had comparable kinetics to most S. cerevisiae strains at 25 °C (Figure 1, analysis of variance (ANOVA) results in Table S4, S5)
The paucity of differences between S. cervisiae and S. uvarum strains in their fermentation kinetics, sugar use, ethanol production, glycerol production and the differences we found among strains in the production of unique volatile compounds, highlights the potential of our S. uvarum strains to be used as commercial strains in the future
Summary
While many factors affect the final aromas and flavours of wine, including grape varietal, available sugars, assimilable nitrogen, pH and fermentation temperature, different yeast strains can impact wine quality by producing different concentrations of volatile compounds (Fleet, 2003; Romano et al, 2003). The unique consortia of microorganisms on the grapes can help start the process of alcoholic fermentation, sometimes persisting well into the fermentation and may even take over both spontaneous and inoculated fermentations, adding character to wines (Bokulich et al, 2013; Lange et al, 2014; Mas et al, 2016; Morgan et al, 2019a) One such yeast species is Saccharomyces uvarum, which is typically described as a cryotolerant yeast that produces more fruity aromas, adds body (Alonso-del-Real et al, 2017; Hu et al, 2018; Varela et al, 2017) and reduces the amount of acetic acid in wine (Kelly et al, 2020). The high genetic diversity of S. uvarum found in this region provides an opportunity to explore the potentially wide range of metabolic functionality in this species
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