Impact of simultaneous fermentation with Saccharomyces cerevisiae and Torulaspora delbrueckii on volatile and non-volatile constituents in beer

This work investigated the compatibility and performance of commercial strains of Saccharomyces cerevisiae (S-04) and Torulaspora delbrueckii (Biodiva) for simultaneous beer fermentation at inoculum ratios 1:2 and 1:20. Based on the fermentation kinetics, metabolic interactions between the strains were evident and dependent on the inoculum ratio. In particular, a marked retardation of strain S-04 was observed at 1:20 ratio while an early cell death of strain Biodiva was noted at 1:2 ratio. The rate of sugar attenuation positively correlated with strain S-04's inoculum size although degree of attenuation and ethanol production for all co-culture beers were comparable to the conventional S-04 monoculture beer. Generally, amino acid assimilation in co-culture beers was more extensive compared to that in both monoculture beers. As for the volatiles, mixed cultures yielded significantly higher amounts of ethyl decanoate and ethyl dodecanoate as well as citronellyl acetate (P < .05). Specifically at 1:2 ratio, ethyl octanoate production was significantly higher while 1:20 ratio beers were characterised by a good fusel alcohol production but higher acetaldehyde amounts. Overall, co-inoculated beers at both ratios displayed evident potential of enhancing the aroma profile of specialty beers.