Population dynamics of wine yeast during spontaneous and guided fermentations and the expression of stress genes as affected by interactions between different strains of yeasts.

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Primary fermentation, which is responsible for ethanol production, is mainly conducted by different strains of Saccharomyces cerevisiae. At an operational scale, primary fermentation is conducted in large tanks, which involves using either spontaneous or guided fermentation. In spontaneous fermentation, the must is exposed to the resident yeast population, whereas in guided fermentation, a commercially available S. cerevisiae yeast starter or active dry yeast (ADY) strain is added. Our spontaneous fermentation studies, conducted on a Pinot Noir variety at Quails' Gate Estate Winery (QGEW) in British Columbia, Canada show that ADY strains are the dominant strains fermenting Pinot Noir must, as opposed to indigenous yeast strains. These findings are in contrast to those from traditional wine-producing regions where indigenous yeast strains tend to dominate. We also showed, at the end of guided fermentation, that the inoculant, ADY strain Lalvin® RC212, was equally dominant with a contaminant ADY strain Lalvin® ICV-D254. This data supports recent traditional wine region findings that multiple strains of S. cerevisiae are often present in guided fermentations. However, in traditional wine regions, contaminant strains tend to be indigenous strains, whereas in our studies, they are comprised of relatively aggressive ADY strains. Our results point to the idea that North American wineries are unique, in that ADY stains dominate spontaneous and guided fermentations and that S. cerevisiae contaminants of guided fermentation tend to be ADY and not indigenous stains. This proposed research program, with respect to yeast strain dynamics and their expression of stress genes in fermenting wine, will help to determine whether this uniqueness is valid by expanding our knowledge to multiple North American wineries. Our main objectives are to: 1) compare yeast strain dynamics of wine between different years, wineries, and stages of fermentation; 2) compare the total yeast community between different stages of fermentation; 3) determine the source of ADY yeast stains in guided and spontaneous fermentations; and 4) compare the expression of stress genes from yeasts, which are subjected to and not subjected to competition from other ADY strains.