Sulfur dioxide is added before the onset of alcoholic fermentation at most commercial wineries to prevent growth of spoilage microorganisms and help create an environment that promotes rapid colonization of the grape must by Saccharomyces cerevisiae. S. cerevisiae is a winery-resident yeast and is rarely found on healthy grapes in the vineyard. It performs the bulk of alcoholic fermentation and is a major contributor to the final aroma and flavor of wine. As such, it is extremely important to understand how the winemaker’s addition of sulfur dioxide at crush can indirectly impact the strains of S. cerevisiae conducting alcoholic fermentation. This study investigates the effects that four different levels of initial sulfur dioxide addition (0, 20, 40, or 80 mg/L SO₂) have on the S. cerevisiae strains present during spontaneous fermentations of two grape varietals at two Okanagan wineries. Yeast isolates collected from samples taken throughout fermentation were identified at the strain level using microsatellite analysis. S. cerevisiae strain composition was significantly impacted by the level of SO₂ added at crush. Each SO₂ treatment had a significantly different strain composition at each winery, and each winery had a completely unique strain composition. The dominant strains throughout fermentation (those comprising at least 10% of the relative strain abundance) were commercial strains at both wineries, with the exception of one strain at one winery, which was of unknown, assumed indigenous, origin. Sensory analysis was conducted at one winery and sensory differences were found between treatments. The results of this study highlight the dominance of commercial strains in commercial winery environments and demonstrate that initial sulfur dioxide addition indirectly alters the S. cerevisiae populations conducting spontaneous fermentations, resulting in altered sensory characteristics.

Funding Support: National Sciences and Engineering Research Council of Canada (NSERC), British Columbia Wine Grape Council (BCWGC)