Effect Of Nutrition Supplementations In High Gravity Wort On Fermentation Performance Of Brewer's Yeast

Although beer high gravity brewing technology can greatly increase productivity,reduce energy consumption,labor,and save production costs on the basis of original equipment,its process disadvantages,such as:the damage to yeast caused by high osmotic pressure and high ethanol concentration limits the growth of cells,resulting in reduced yeast vitality,slower fermentation speed,lower ethanol content,changes in flavor composition.Nutrients supplementations in high gravity wort has been proven to effectively improve the fermentation performance of yeast during high gravity brewing.This research is based on the previous research in the laboratory.Branched chain amino acids(Val,Leu,Ile)and basic amino acids(Arg,Lys,His),jujube juice and jujube polysaccharides were added to high gravity wort for beer fermentation,respectively.The effects of nutrient supplementation on yeast fermentation performance and beer flavor during high gravity brewing was studied by analyzing related physical and chemical indicators.The main findings were as follows:(1)The effects of three branched chain amino acids(Val,Leu,Ile)and three basic amino acids(Arg,Lys,His)on yeast fermentation performance were studied.The results showed that the six amino acids could improve the fermentation performance of yeast during high gravity brewing.Theloss of all amino acid supplementation groups was higher than the control group,and the fermentability and ethanol production were significantly higher than the control group(P<0.01).The Arg,Val,and Leu groups performed better,withloss of 91.2 g/L,92.4 g/L,and 92.7 g/L,and fermentability of82.93%,83.65%,and 82.95%,respectively.The ethanol production was 11.83%(V/V),11.97%(V/V)and 11.90%(V/V),respectively.In addition,Arg supplementation could significantly increase the total number of yeast cells(1.64×10~8 cells/m L)(P<0.05),and His supplementation could significantly increase cell viability(82.69%)(P<0.05).Basic amino acids supplementation could greatly increase the content of isobutanol,isoamyl alcohol and other higher alcohols.Leu supplementation greatly increased the content of isoamyl acetate.Lys supplementation could reduce the total higher alcohol content.(2)The effects of jujube juice supplementation on yeast fermentation performance during high gravity brewing were studied.The results showed jujube juice supplementation could improve the fermentation performance of yeast.High gravity wort supplemented with30%and 35%jujube juice showed the best effect.Theloss of each jujube juice group was higher than that of the control group.Supplementation with different proportions of jujube juice could significantly increase the fermentability(P<0.01).In addition,15%,30%and 35%jujube juice supplementations could significantly increase ethanol production(P<0.05).Furthermore,30%and 35%jujube juice supplementations exhibited better effect.The fermentability were 88.18%and 87.90%,and the ethanol production were 11.30%(V/V)and 11.20%(V/V),respectively.Supplementation with jujube juice could significantly affect the color value of beer:as more jujube juice was added,the L*value of beer gradually decreased,the a*value and b*value gradually increased,and the difference from commercial beer and the control group was also bigger.Compared with the control group,19 new flavor substances were detected in all jujube juice groups,and jujube juice reduced the alcohol-ester ratio of beer and the formation of higher alcohols.Therefore,supplementation with jujube juice could improve the fermentation performance of yeast in high gravity brewing process,and could affect the color value and beer flavor.(3)The effects of different amounts of jujube polysaccharide on yeast fermentation performance during high gravity brewing were studied.The results showed that jujube polysaccharide could not significantly promote fermentation performance of yeast,but it showed a positive effect on the color value and beer flavor.Supplementation with jujube polysaccharide could produce rich foam during fermentation,and reduceloss to a certain extent.Jujube polysaccharide had no effect on ethanol production,but it significantly reduced the fermentability(P<0.01).Among all the groups,the control group showed the best fermentation performance,and the fermentability and ethanol production reached 84.66%and 10.8%(V/V),respectively.The supplementation of jujube polysaccharide reduced the L*value,and increased the a*value and b*value of beer.The higher the amount of jujube polysaccharide,the greater the difference between the color value of beer and the control group.The proportion of alcoholic substances in the total flavor substances decreased as the jujube polysaccharide content increased.In all jujube juice supplementation groups,14 new flavor substances were detected compared with the control group.