Growth and metabolism of non-Saccharomyces yeasts isolated from Washington state vineyards in media and high sugar grape musts

Utilization of carbohydrates and amino acids/ammonium by selected non-Saccharomyces yeasts and impacts on alcoholic fermentation was evaluated using media and high sugar grape musts (>270 g/L). Consumption patterns of single cultures were ascertained in synthetic media and a Chardonnay grape must. While the non-Saccharomyces species maintained >106 cfu/mL after >40 days, concentrations of residual sugars ranged from 103 g/L (Wickerhamomyces anomalus) to 155 g/L (Candida californica), amino acids and ammonium were generally depleted (>85%), and excessive amounts of volatile acidity (>0.8 g/L) were sometimes produced (e.g., C. oleophila). To minimize problems associated with nutrient depletion before alcoholic fermentation, non-Saccharomyces yeasts were inoculated six days ahead of S. cerevisiae into Syrah grape musts. Syrah ferments inoculated with C. californica or Metschnikowia pulcherrima contained lower concentrations of residual sugar and ethanol compared to those with only S. cerevisiae. Furthermore, the presence of non-Saccharomyces yeasts influenced concentrations of glycerol and volatile aroma compounds. These results suggested potential use of some non-Saccharomyces yeasts towards reducing alcohol concentrations without risking slower alcoholic fermentations.