Several Fine Brewer's Yeast Strain Screening And Their Pilot Scales

Brewer's yeast strain is the key to the beer brewage production. So it is an important task to select an excellent yeast strain. In the study, physical and chemical mutagenesis and protoplast fusion technique were used to select strains with low-yielding diacetyl, acetaldehyde, total higher alcohols and other excellent characteristics.The strain JY2-2 with excellent fermentation characteristics was obtained from strain XB05 after mutation by semiconductor laser. The results of tests carried out in the 500L, 120t, 240t and 360t fermentation tanks indicated that the mutant JY2-2 was of strong ability of fermentation and diacetyl removal. The contents of diacetyl, acetaldehyde and total higher alcohols in the fermented liquid were relatively low and these characteristics were stable. The sensory evaluation of the beer produced by the mutant JY2-2 was very nice. The strain JY2-2 has been applied to the beer brewing.Three strains EY2-4, EY2-9 and EY4-2 were obtained from strain XB05 after continual mutation by ultraviolet and EMS and screening anti-diacetyl strains by flask fermentation.The results of tests carried out in 500L fermentation tanks and productive tests showed that the mutant EY4-2 was of strong ability on diacetyl removal and had the advantage in rising pH value of the fermented liquid. The sensory evaluation of the beer produced by the mutant EY4-2 was nice. Strain EY4-2 is of well applied prospect on the beer brewing.The protoplast fusants were constructed with the protoplasts of UV-inactivated X6-5-3 and heat-inactivated JY2-3. The conditions of protoplast fusion between X6-5-3 and JY2-3 were researched with orthogonal experiment. Seven fine strains SRY21,SRY34,SRY58,SRY70,SRY73,SRY74 and SRY75 were obtained after selection. The cell volume, biomass, DNA contents of them were measured in comparison with their parental strains and the results showed that these strains were fusants. The fermentation tests of strain SRY21 were conducted in the 500L fermentation tanks. The results indicated that strain SRY21 was of strong fermentative ability (fermentative degree of 69.6%), the contents of diacetyl, acetaldehyde and total higher alcohols were 0.0223 mg/L, 3.80 mg/L and 63.42 mg/L at the end of the fermentation, respectively. The sensory of the beer SRY21 produced was relatively nice.