Control And Regulation Of Diacetyl And Higher Alcohols In Beer Fermentation

Diacetyl and higher alcohols are important component of beer favor. Diacetyl is signal products of ripeness of beer fermentation and proper content of higher alcohols could make beer products full and mild in taste, but excessive higher alcohols not only bring beer peculiar smell but also make beer toxic and ebriety caused by alcohols, so superscale of diacetyl and higher alcohols had become restrictive factors and outstanding contradictions of improving beer qualities, especially in producing low cost beer products fermented by elevating fermentation temperature, shortening fermentation period and increasing content of subsidiary materials. In this study, the Saccharomyces cerevisiae strains YZB and YZD were obtained by screening of diacetyl and tribenuron-metyl resistance, whose diacetyl summit value reduced to 0.36mg.L-1 in small scale amplified fermentation experiment, which was 42%~44% lower than that of original strains. The final diacetyl content was 0.07~0.08 mg.L-1 and the real fermentation degree was varied between 65.8% and 66.1% after fermentation, meanwhile, the other fermentation characteristics remained tiny change. Also genetic characteristics of obtained strains were stable after 7 generations of inoculation.Based on the higher alcohols and lactic acid metabolism theory, a method was developed to low higher alcohols capability Saccharomyces cerevisiae strains by screening high lactic acid dehydrogenization enzyme activity in this study. By this way, the strain YZD with low diacetyl level used as original strain was selected on lactic plate, wort-CaCO3 plate and TTC plate, and the new strain was obtained, named Y1110, which the higher alcohols in final fermentation products was decreased by 28.7% than that of original strains, but the diacetyl level and other fermentation characteristics remained unchanged and it also showed stabilization after 8 generations. The summit and final value of diacetyl of strain Y1110 during the period of fermentation were 0.36mg.L-1 and 0.08 mg.L-1 respectively and its accumulated content of higher alcohols could be reduced to 70.2mg.L-1.