Breeding Of Beer Yeast With Low Yield Of Fusel Alcohols At High Temperature

In this paper, the formation mechanism of fusel oil in beer yeast, breeding of beer yeast with low yield of fusel alcohols and beer flavor stability were studied.Beer yeast (Saccharomyces cereviase) SC-1-SC-7 were employed for fermentation trials. The fermentation characteristics were determined, as well as the production of fusel oil and diacetyl respectively. SC-2 was selected as the parent strain for its better flocculability ability, the higher fermentation degree and that the lower yield of fusel oil and diacetyl.The effect of branched-chain amino acid on fusel oil production by SC-2 in beer fermentation was studied. The conclusion showed that the effect of leucine was the most remarkable. Under the instruction of metabolic control theory, the screening of leucine auxotroph was determined as the method of selecting the mutant strain of low-yield fusel oil.After the UV treatment to the parent strain SC-2, eleven strains were selected with the character of leu- and four among them were especially good in this respect, for their resulting beers all contained up to 20% less total fusel oil compared to the parent strain SC-2. Through the comparison of the fermentation characteristics, the diacetyl production and the effect of a -amino nitrogen content etc, strain MS-11 was selected as the best one, for its yield of total fusel oil was lower by 25.47%, diacetyl and other fermentation characteristics were almost invariable. In the fermentation trial with the mutant strain MS-11 at high temperature, the conclusion showed that the high temperature quickened up the fermentation process and diacetyl deoxidizatioa Its yield of fusel oil was 65.35mg/L at 14 C, which was near to that of the parent strain SC-2 63.24mg/L at 9 C, moreover, the diacetyl content was reduced by 15.13%.Comparing with SC-2 at 9 C, the result of beer fermentation by MS-11 at 14 C indicated that the TBA value decreased 12.08% and the RSV value increased by 29.63%, which showed that the beer flavor stability was improved.The experiment was quite significative for its quickening up fermentation process and yielding ambrosial and lasting beer at high temperature.