Screening And Application Of The Fine Saccharomyces Cerevisiae Strains With Appropriate Flocculablity

Brewing yeast Hp34is low-yielding acetic acid saccharomyces yeast, and the velocity of decline of sugar concentration is fast. The acid feeling of the beer produced by Hp34was coordinated, the sensory was soft and refreshing, but flocculation is poor in large-scale production.Hp34strain using selection of spontaneous mutation^tries to select a stable strain with appropriate flocculation and good traits of the initial strain. The results showed that flocculation ability of strains, select by directly with Tablet separation was proximity to the original strain. The continuous culture method can improve flocculation ability of parent strain from17%to27.5%.There is a certain gap with flocculation (37%) of beer industrial production strains.In order to screen the target strains, parent strain was mutated by EMS, and deal with continuous culture. The method screened out12mutants with flocculation more than35%, according to the acetic acid in fermentation liquid of mutant strains and other flavor compounds and the determination results of fermentation performance, the research selects a fine strain S16with appropriate flocculation, over the study of laboratory yeast strains by the small pilot-scale low-temperature fermentation and genetic stability, we found that acetic acid, diacetyl, fermented degree, and flavor indicators of the mutant S16were as much as that of the original strain. Its capacity of flocculation amounted to39.6%, which was2.21times than the original strain, and the mutant strain had the hereditary stability.Compared with parent strain and beer industrial production strain study and analysis the feasibility of this appropriate flocculation saccharomyces yeast used in beer production, pilot fermentation has carried out in this research, we got comprehensive evaluation from both the fermentation performance and sensory evaluation. The result shows that the mutant S16keep the fine fermentation characteristics of original strain Hp34, and improve the flocculation characteristics. At the end of fermentation, the number of yeast cells in the fermentation can be decreased rapidly. In the fermentation characteristics, mutant S16is superior to the beer industrial production strain X. The beer produced by mutant S16get fine quality of soft and refreshing, the acid feeling get coordinated, in line with beer characteristics of saccharomyces yeast.In the experiment also studied the influence of yeast strains on the formation of organic acid in process of beer fermentation. Results showed that the yeast strains were significant relationship with the contents of the main organic acids, and directly affect the content of the main organic acids in process of beer fermentation. The contents of acetic acid, lactic acid, succinic acid and pyruvic acid increased significantly, and the contents of citric acid have a little difference with fermentation process. Through the action of organic acid, the yeast also has an important effect on pH, total acid, acid feeling. The analysis found that acetic acid is the greatest impact on pH, total acid, and acid sense.Followed by succinic acid (malic acid),lactic acid, citric acid, pyruvic acid.