Changes

Interestingly, we observed a potential dose-dependent decrease in isoamyl acetate (banana) concentration at 3 weeks (Figure 3). Therefore, higher pitch rates of ''Brettanomyces'' in secondary fermentation may metabolize isoamyl acetate faster, reducing the concentration of this ester. Thus, high pitch rates of ''Brettanomyces'' could be useful to quickly reduce isoamyl acetate in beers where this flavour is undesirable. We also observed a more subtle dose-dependent decrease in concentration of two other acetate esters at high ''Brettanomyces'' pitch rate, ethyl acetate (pear, solvent) and phenethyl acetate (honey, yeasty, floral) (Figures 3, 4). Interestingly, we observed higher concentration of these esters in the low pitch rate sample. Confirming this phenomenon and its potential sensory ramifications would require an expanded experimental design including replicates. Ultimately the differences are subtle, and it is likely that these do not have significant effects on the sensory character of the resultant beers. Concomitant with the slight reduction in acetate esters by addition of ''Brettanomyces'', we also observe slight increase in volatile acetic acid concentration with pitch rate (Figure 5), but the concentration regardless is well below the sensory threshold for acetic acid. Thus it is possible that acetate esters can be hydrolyzed by ''Brettanomyces'' under anaerobic conditions via an unknown mechanism. We await sampling at the 3 month timepoint to assess whether these trends continue and become more clear.

We were not able to identify any clear trends in levels of volatile organic acids (Figure 5). These compounds typically cause off-flavours in immature ''Brettanomyces'' fermentations.