Using Non-Saccharomyces Yeast to Modify Acidity during Wine Fermentations from Vitis Hybrid Grapes Grown in a Warm Region

Background and goals Warm temperatures during the grapegrowing season can negatively affect the acidity of resulting wine. In an attempt to modify the acidity and other wine attributes ultimately affected by warm grapegrowing climates, interest in using non-Saccharomyces yeast during fermentation has increased.

Methods and key findings In 2020 and 2021, Arkansas-grown Chambourcin (Vitis hybrid) red wine grapes were hand-harvested (181 and 168 kg, respectively) for wine production. Grapes were randomized into batches, crushed, and destemmed. In both years, four inoculation treatments were conducted in duplicate using Saccharomyces cerevisiae with and without malolactic cofermentation (SC-MLF and SC, respectively), and sequential inoculation with Lachancea thermotolerans and S. cerevisiae with and without malolactic cofermentation (LT-SC-MLF and LT-SC, respectively). Across both years, total soluble solids, pH, and titratable acidity (TA) averaged 19.2%, 3.5 pH, and 7.5 g/L, respectively, at harvest. Evaluations of treatments were done on must/wine during fermentation at 21°C. In both years, all treatments completed alcoholic fermentation by day 6 with ethanol ~10%. From day 0 of fermentation to day 5 in both years, LT-SC and LT-SC-MLF treatments yielded average reductions in pH by 0.2 units (from pH 3.5) and malic acid of 1.0 g/L (from 4.0 g/L), and increases in TA (expressed as tartaric acid) of 5.6 g/L (from 7.3 g/L), and lactic acid of 5.8 g/L (from 1.0 g/L).

Conclusions and significance In this study, fermentations with L. thermotolerans and Saccharomyces yeasts produced Chambourcin wines with lower pH and higher TA, suggesting the potential ability of non-Saccharomyces yeast to decrease the use of tartaric acid and sulfur dioxide prior to fermentation and during wine production.