Aroma compounds profile is affected by the initial yeast ratio in wort co-fermentations

In recent years, the boom of the craft beer industry refocused the biotech interest from ethanol production to diversification of beer aroma profiles. This study analyses the fermentative phenotype of a collection of non-conventional yeasts and examines their role in creating new flavours, particularly through co-fermentation with industrial Saccharomyces cerevisiae. High-throughput solid and liquid media fitness screening compared the ability of eight Saccharomyces and four non-Saccharomyces yeast strains to grow in wort. We determined the volatile profile of these yeast strains and found that Hanseniaspora vineae displayed a particularly high production of the desirable aroma compounds ethyl acetate and 2-phenethyl acetate. Given that H. vineae on its own was a poor fermenter, we carried out mixed wort co-fermentations with a S. cerevisiae brewing strain at different ratios. The two yeast strains were able to co-exist throughout the experiment, regardless of their initial inoculum, and the increase in the production of the esters observed in the H. vineae monoculture was maintained, alongside with a high ethanol production. Moreover, different inoculum ratios yielded different aroma profiles: the 50/50 S. cerevisiae/H. vineae ratio produced a more balanced profile, while the 10/90 ratio generated stronger floral aromas. Our findings show the potential of using different yeasts and different inoculum combinations to tailor the final aroma, thus offering new possibilities for a broader range of beer flavours and styles. IMPORTANCECraft brewing underwent an unprecedented growth in the last years due to customer demand for more unique and complex beverages. Brewers started to explore innovative fermentation methods using new ingredients, different brewing conditions, and new yeasts to explore a larger flavour landscape. The use of non-Saccharomyces yeasts has emerged as an effective strategy to produce novel distinct flavour profiles, however, knowledge regarding their fermentation performance and volatiles production is still limited, which hinders their industrial application. In this study, we expand on the knowledge of several non-Saccharomyces yeasts in terms of their brewing application and highlight the potential of H. vineae in co-fermentation with S. cerevisiae for producing unique fruity beers with a standard ethanol content. Our findings provide the craft beer industry with a new strategy to produce distinctive fruity beers.