Due to changes in viticultural practices coupled with increasing temperatures in growing regions, sugar concentrations in grape musts have increased, leading to increased ethanol concentrations in the resulting wines. A natural component of the grape berry microbiome, non-Saccharomyces yeasts have the potential to reduce ethanol yield through respiration of glucose/fructose. The objective of this research was to identify native yeast strains that do not express the biochemical Crabtree Effect whereby sugars are fermented, not respired, regardless of oxygen availability. Non-Saccharomyces yeasts were screened using a high Brix Merlot grape juice (310 g/L 1:1 mixture of glucose/fructose and 270 mg/L yeast assimilable nitrogen) with and without aeration. After six days, aliquots were inoculated with a commercial strain of Saccharomyces cerevisiae to finish fermentation. While most aerated fermentations consumed less sugar and more nitrogen than nonaerated ones, some isolates also yielded less ethanol. Native strains of Candida spp. exhibited the greatest ethanol reduction under aerated conditions but accumulated excessive amounts of acetic acid that will limit industrial application. The native Metschnikowia pulcherrima isolate is more promising, giving a similar reduction in ethanol concentration without excessive acetic acid production. Though screening results are encouraging, this study shows that aeration and available nitrogen must be optimized to reduce potential deleterious effects on the wine’s sensory profile prior to industry application.

Funding Support: Wine Advisory Committee of the Washington Wine Commission, Agricultural Research Center, WSU-CAHNRS