UBC Theses and Dissertations

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UBC Theses and Dissertations

The effect of sulfur dioxide and alternative fermentation techniques on the microbial communities and sensory profiles of wine Morgan, Sydney Christian


Modern winemaking often involves the addition of sulfur dioxide (SO₂), to remove potential spoilage microbes from the grape juice, and the addition of commercial wine yeasts, to ensure a successful and timely completion of alcoholic fermentation. However, consumer demand is shifting towards low-SO₂ wines, and wines fermented by a collection of indigenous yeasts and bacteria. Many winemakers wish to produce these wines for their customers, but there is a current lack of research into the relative risks and rewards of these winemaking strategies. We investigated these topics, and found that both SO₂ addition and inoculation technique can significantly influence the fungal and bacterial communities and the sensory profiles of commercially-produced wines. Fermentations conducted without SO₂ were found to contain more vineyard-derived microorganisms and produced more fruity characters, while the fermentations conducted with SO₂ produced wines with less-desirable characteristics. Pied de cuve inoculation had a limited effect on the wine microbial communities and was inhibited by the addition of SO₂; when it persisted, it resulted in slower fermentations, and produced wines with more sweetness and body as compared to wines that did not receive the pied de cuve inoculum. At one commercial winery, we identified a highly diverse indigenous population of Saccharomyces uvarum, a yeast that is related to the main winemaking yeast, Saccharomyces cerevisiae. S. uvarum was able to compete with a commercial S. cerevisiae strain in controlled fermentations, and produced wines with a unique composition of aroma-active volatile compounds, showing its potential to be used as an indigenous yeast inoculum for locally-made wines. In summary, we showed that both SO₂ addition and fermentation technique (uninoculated or pied de cuve inoculation) can alter the microbial communities and sensory profiles of commercial and laboratory-made wines, and reported an indigenous yeast population in the Okanagan Valley winemaking region.

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