Fungal Diversity and Dynamics during Grape Wine Fermentations with Different Sulfite Levels and Yeast Inoculations

Microbial communities during grape wine fermentations are diverse and dynamic. High-throughput sequencing (molecular methods enabling precise identification of microbial communities) was used to identify fungal diversity during fermentation of grape juice with different sulfite levels and yeast inoculations. Fermentation (0, 14, and 21 days) was evaluated in two grape varieties, Noble (Vitis rotundifolia) and Vignoles (Vitis hybrid), fermented at three sulfite levels (0, 10, and 20 mg/L) with three yeast inoculations (uninoculated, Saccharomyces cerevisiae, and Torulaspora delbrueckii). Fungal taxonomy of both varieties included six to seven phyla and 115 to 129 genera. The indigenous microbiota was affected by sulfite level and yeast inoculation and varied by grape variety. Sulfite levels had minimal effect on fungal communities but did affect fermentation dynamics. Increasing sulfite additions did not affect the fermentation performance of S. cerevisiae but did affect the fermentation of uninoculated juice and T. delbrueckii-inoculated juice. The primary fungal genera (Podosphaera, Candida, Phialemoniopsis, and Meyerozyma)—those present at a relative abundance >1%—were the same for both varieties but at different relative abundance. Similar fungal diversity patterns were observed for both varieties, with a decrease in diversity at day 14 and an increase at day 21 of fermentation. Juices inoculated with T. delbrueckii were rapidly colonized by Torulaspora spp. at day 0 for both varieties, whereas Saccharomyces spp. dominated by day 14 when inoculated with S. cerevisiae, especially in Noble. The most abundant genera in uninoculated juice were Hanseniaspora and Zygoascus for Noble and Hanseniaspora and Saccharomyces for Vignoles. Understanding grape juice microbial communities and the dynamics of these communities during fermentation provides insight for wine production using spontaneous fermentations or non-Saccharomyces species and information on the effect of sulfur dioxide on these novel fermentations.