UBC Theses and Dissertations
Dominance of indigenous Saccharomyces uvarum in spontaneous wine fermentations conducted in the Okanagan Valley McCarthy, Garrett
The majority of wines are produced by inoculated alcoholic fermentations using commercialized strains of Saccharomyces cerevisiae, yet there is a growing trend in winemaking to perform spontaneous fermentations, which rely on microbiota present on grape berries, and/or on winery surfaces and equipment. An advantage for spontaneous over inoculated fermentation is a more complex sensory profile due to a wider range of metabolites from differing yeast species, which may help to define the regional identity of the wine. Once the spontaneous fermentation progresses into the mid and late stages of fermentation, ethanol-tolerant S. cerevisiae strains usually dominate. Contrarily, previous studies in our lab showed that an indigenous yeast, Saccharomyces uvarum, can dominate over S. cerevisiae during spontaneous Okanagan Chardonnay fermentations. My objectives were to: 1) determine if S. uvarum was again part of the fungal community in spontaneous Chardonnay fermentations; and if so; 2) develop an improved classification method for S. uvarum strains; 3) determine the degree of genetic diversity of the S. uvarum populations in spontaneous Chardonnay fermentations, which differ in their grape origin; and 4) determine whether S. uvarum was part of the fungal community on grapes from different vineyards of the Okanagan Valley wine region. Using Illumina high-throughput sequencing, I found S. uvarum was again dominant over S. cerevisiae in all winery fermentations, similar to findings in 2015 from spontaneous fermentations in the same winery. Using culture-dependent methods, I performed S. uvarum strain analysis with a novel, 11-loci microsatellite multiplex screen, and used Bruvo genetic distance to classify multi-locus genotypes into strains. I identified over 200 multi-locus genotypes and classified them into over 50 unique strains from winery fermentations that differed significantly in composition between treatments comprising grapes from two Chardonnay vineyards. As well, high-throughput amplicon sequencing revealed the presence of S. uvarum throughout all four vineyard locations spread across the Okanagan Valley wine region. My results indicate there may be commercial interest in using S. uvarum as a potential alternative to S. cerevisiae, which is typically the species used in winery fermentations.
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