Hybridization Breeding Of High Tolerance Saccharomyces Cerevisiae And Study On The Brewing Process Of High Gravity Beer

Beer brewing yeast S-04,US-05 and winemaking yeast CY3079,RC212 were selected as experimental research objects in the present study.Yeast strains with high alcohol tolerance,high osmotic pressure and excellent fermentation performance were cultivated by cross breeding technology,and yeast strains suitable for brewing Imperial Stout special beer were screened by combining fermentation performance,physical and chemical indexes and flavor substance content.On the basis of determining yeast strains,the effects of yeast inoculation amount,main fermentation temperature and hop addition amount on beer taste and flavor were explored through single factor analysis and sensory score,and the fermentation conditions of Imperial Stout special beer were optimized by response surface analysis.The specific research results are as follows:(1)After the original strain was activated by wort medium and inoculated into Mcclary medium,beer yeast strain S-04 and US-05 reached the highest sporulation rate at 28?for 6 days,which were 67.23%and 72.69%respectively.Wine yeast strain CY3079 and RC212 reached the highest sporulation rate at 26?for 7 days,which were31.67%and 33.56%,respectively.Through haploid separation and identification,34haploids were obtained,among which 17 haploids of type a,accounting for 50%,and 17haploids of type?,accounting for 50%.According to haploid strain screening experiment,haploids S-1,U-7,C-5,C-6,R-4 and R-9 were used as high-tolerance hybrid parents,and 85 hybrid yeast strains with good growth were obtained after hybridization.(2)After pressure screening and wort fermentation experiments,combined with yeast fermentation performance and flavor substances produced by metabolism,hybrid yeast strain UR-2 was determined to be more suitable for high-concentration beer brewing.Compared with the original strains of wine(CY3079 and RC212),the actual fermentation degree increased by 7.2%and 4.1%,the alcohol content increased by24.7%and 23.2%,and the residual sugar decreased by 5.4%and 14.5%.The content of alcohols and esters produced by metabolism of strain UR-2 is high and the proportion is coordinated,which can make beer taste balanced and mellow,and is suitable for beer very high gravity fermentation.(3)On the basis of single factor,taking sensory score as response value,response surface experiment was designed to optimize the brewing process of Imperial Stout special beer.The results are as follows:the inoculation amount of yeast is 2.75×10~7cells/mL,the main fermentation temperature is 21.0?,and the hop addition amount is1.06g/L.Under these conditions,the sensory score of Imperial Stout special beer is high,reaching 93 points,which is only 0.21%worse than the predicted value of regression model.Under the optimum fermentation conditions,a 50L fermenter was used.The alcohol content of Imperial Stout special beer was 11.2%vol,the actual fermentation degree was 69.5%,the residual sugar was 5.06 g/100mL,and other physical and chemical indexes reached the national standard.The finished beer is brown in appearance,soft and delicate in foam,good in foam retention,strong in killing ability,low in diacetyl content,free of peculiar smell,high in bitterness value,compatible with high alcohol content,full-bodied,rich in burnt malt and tropical fruit flavor,slightly sweet,and is a strong beer with unique characteristics.