Exploring the phenotypic space of non-Saccharomyces wine yeast biodiversity

Tremendous microbial diversity exists in vineyards, and the potential to harness this diversity for novel mixed or pure starter cultures for wine fermentation has received significant attention in recent years. However, most studies are limited to a small subset of strains and species. Here we present data from a systematic screen of 91 yeast isolates from South African grape must and vineyard samples for oenologically relevant traits. One focus area was finding non-Saccharomyces isolates showing both reduced ethanol yields, as well as improved aromatic characteristics. Of the 91 isolates evaluated initially, 21 showed lower ethanol yields when compared to commercial wine yeast strain controls. Collectively, the metabolic data (primary fermentation and secondary aroma compounds) highlight the enormity of the 'phenotypic space' of yeast communities in South African vineyards. The data also emphasise intraspecies variability, challenging our concept of species typicity. Of particular oenological interest was the ability of several isolates to produce high levels of terpenoid compounds. A few strains were ultimately found which showed a substantial reduction (>1.5%) in the final ethanol content of sequential fermentations, as well as unique aroma compound production profiles. Four of these strains were selected for comprehensive wine trials in both red and white grape musts, complete with microbial, chemical and sensory analyses of the red wines. This presents, for the first time, a full bench-to-bottle characterisation of non-Saccharomyces strains showing the most potential for commercial application. The findings of this study enlarge the potential range of oenological applications for non-Saccharomyces yeast, while also suggesting the potential usefulness of several yeast species that have previously not been considered for winemaking applications.