Breeding And Application Of Brewer’s Yeast In Very-high-gravity Brewing

The very-high-gravity brewing has become the main trend of beer fermentation. This technology, on the basis of high gravity brewing, can reduce energy sources consumption and improve equipment utilization, effectively. It has been popularized in foreign countries but less application in China. One of the main reasons is the lack of excellent beer yeast for very-high-gravity brewing.In this paper, the starting yeast strain SC-I was deposited at Bioengineering Laboratory of Yantai University. The method of selective culture combined with progressive domesticated screening was used to obtain two yeast strains, SC-8and SC-9, which suitable for very-high-gravity brewing. The results showed that the strain SC-8could grow well and fast fermentation in worts of12%vol alcohol concentration and resist osmotic pressure by23°P worts. And the strain SC-9could grow well and fermentation in worts of13%vol alcohol concentration and resist osmotic pressure by22°P worts.Taking into account the fact that high alcohol content has more unfavorable effects to brewer’s yeast than high osmotic pressure, the strain SC-9was selected for11°P and22°P worts fermentation in the volume of10L fermenter in the paper. The changes of various parameters of fermentation and physical-chemical indices of finished beer were analyzed. The results showed that the fermentation period of very-high-gravity brewing by22°P worts was extended. However, the variation of the various parameters in the22°P worts fermentation process was the same as11°P worts. The real degree of fermentation was up to75.07%, slightly lower than the conventional11°P worts (77.06%). The alcohol content of finished beer was9.62%vol,2more times than the11°P finished beer (4.77%vol). In the end of fermentation, the pH value of fermentation broth was4.4, meeting the requirements of finished beer to pH. The peak of diacetyl content was0.89mg/L, higher than that the diacetyl content of finished beer,0.139mg/L, in the range of the threshold (0.15mg/L). Therefore, the strain SC-9was applicable to very-gigh-gravity brewing by22°P worts. The strain also could be used for the production of conventional beer by dilution technique.