Preliminary Study Of High Alcohol Beer

High alcohol beer with high alcohol content and calories is popular in the world.In this paper, fermentation of beer with alcohol content above8.6%vol and realfermentation degree above70%using very high gravity wort (18°P) has been studied. Lageryeast which could be resistant to glucose repression was selected. The optimal conditions ofmashing process were determined. The fermentation parameters that affect alcohol contentand yeast viability during brewing were analyzed. Main results were as follows:(1)18strains of lager yeast stored in our laboratory were used in18°P wort brewing.Strain Y12with the highest value of real fermentation was selected as original strain forfurther study. Through the steps of domestication with2-deoxy-D-glucose (2-DOG),screening with gradient resistant plates and re-screening, better-performing strain Y12-23which was resistant to glucose repression was identified. Fermentation performances by strainY12-23and Y12were tested in3L EBC tubes with18°P wort at15℃, respectively. Theresults showed that Y12-23had faster fermentation rate as well as higher viability, and theaverage attenuation rate was1.8°P/d,38.5%faster than that of strain Y12. Alcohol contentand real fermentation degree of beer fermented by Y12-23reached7.89%vol and65.69%,respectively. Compared to beer fermented by Y12with alcohol content of7.38%vol,6.9%higher alcohol content was achieved. Meanwhile, Y12-23was substantially equivalent tostrain Y12in terms of the diacetyl reduction and main volatile flavor compounds.(2) Effects of glucoamylase addition, mash time, mash temperature, pH and grist-waterratio on limit fermentation degree and free amino nitrogen content were studied duringmashing. The optimal conditions were as follows: glucoamylase addition was280U/g maltgrist, mash rest time was100min, mash temperature was60℃, mash pH was5.2andgrist-water ratio was1:4. Under these conditions, limit fermentation degree and free aminonitrogen content in wort were76.72%and147.81mg/L, respectively. Alcohol content in beerfermented by Y12-23reached8.26%vol, which was11.9%higher than that of the originalstrain Y12before optimization of mashing.(3) Influences of key factors during fermentation, including fermentation temperature,pitching rate, assimilable nitrogen content and concentration of Zn2+, on yeast viability andalcohol content were also studied. The optimal conditions were as follows: fermentationtemperature was15℃, pitching rate was3.5×107cells/mL, assimilable nitrogen content was1.65g/L, concentration of Zn2+was0.5mg/L. Under these conditions, alcohol content in beerfermented by Y12-23reached8.89%vol,20.5%higher than that of the original strain Y12.Real fermentation degree reached73.80%. Meanwhile, yeast viability after fermentationremained at97%.