Brewing Technology Of Imperial Stout And Its Flavor Substance Analysis

In this thesis,three Ale yeasts(code-named Y1,Y2,Y3)were selected from China-Germany Brewing Technical Center of Qilu University of Technology to conduct a comparative brewing experiment on Imperial Stout beer.The physical and chemical indicators and flavor components of the finished Imperial Stout beer were tested.Finally,sensory evaluation was used to compare and analyze the finished beer brewed by these three types of yeast,so as to select the most suitable yeast for brewing Imperial Stout beer,and applied to the subsequent brewing of Imperial Stout beer;Subsequently,the brewing process conditions of Imperial Stout beer were optimized through a single factor experiment combined with a response surface model to obtain the optimal process parameters;Finally,the 2000 L pilot scale brewing experiment of Imperial Stout was conducted using the most suitable yeast and the best process,tracking various indicators during its fermentation period,and testing the physical and chemical indicators and flavor components of the finished Imperial Stout beer.At the same time,a comparative analysis was conducted combining sensory evaluation with imported Imperial Stout beer on the market.This research has made certain contributions to the development of Imperial Stout beer.Yeast screening results: Y2 yeast has the fastest growth and reproduction rate,but the worst cohesiveness.Y1 yeast and Y3 yeast have slightly lower growth rates than Y2,but Y3 yeast has the best cohesiveness and faster yeast sedimentation;The sugar lowering rate and alcohol production ability of Y3 yeast are slightly higher than those of Y1 yeast,while Y2 yeast has the worst sugar lowering and alcohol blending ability;Y3 yeast has the strongest performance in reducing diacetyl and has the fastest reduction rate.There is a small difference in the ability of Y1 yeast and Y2 yeast to reduce diacetyl,but the reduction rate of Y2 yeast is slower.In summary,Y3 yeast has the best overall performance,while Y1 yeast is at a moderate level without obvious defects.Although Y2 yeast has a fast proliferation rate,its other performance is the weakest.In terms of physical and chemical indicators,there are slight overall differences among the three beers.Y3 has the highest alcohol content and fermentation degree,and the lowest diacetyl content.All other indicators are excellent,so Y3 yeast has good comprehensive performance.In terms of flavor components,the higher alcohol content of Y2 is higher than that of Y1 and Y3,and the alcohol ester ratio of Y1 and Y3 is within the normal range.However,the higher alcohol ester ratio of Y2 may cause symptoms such as headaches for drinkers after drinking;Y3 beer has the highest ester content,therefore it has better ester production performance;The organic acid content and acetaldehyde content in the three beers are all within the standard range,and the dimethyl sulfur content is also below the threshold,with no significant difference.According to sensory evaluation,the quality of Imperial Stout beer brewed by Y3 yeast was the best,with full color,rich foam and mellow body.The alcohol ester flavor and malt flavor were coordinated,without obvious flavor defects.Based on the above experiments and analysis,it is concluded that Y3 is the optimal yeast for Imperial Stout beer brewing,so Y3 is used as the brewing yeast for subsequent experiments.On the basis of selecting the most suitable yeast,using sensory scores as indicators,explore the effects of the proportion of burnt malt added,the proportion of black malt added,and fermentation temperature on Imperial Stout Beer.Firstly,the appropriate parameter range was determined through single factor experiments,and then the response surface model was established to determine the optimal process parameters: the proportion of caramelized malt added was 17.76%,the proportion of black malt added was 7.79%,and the fermentation temperature was 22.19℃.The sensory score of Imperial Stout beer brewed under this process parameter is 92.03.In order to ensure the practicability of brewing in reality,adjustments were made to the optimization parameters: the proportion of burnt malt added was 18%,the proportion of black malt added was 8%,and the fermentation temperature was 22.0℃.On the basis of the process conditions,a 2000 L pilot scale brewing experiment was conducted.After fermentation,the beer was cold stored for 7 days,and various indicators of the finished Imperial Stout beer were tested.After optimization,the physical and chemical indicators of the finished beer met national and market standards.The original wort concentration and alcohol content were classified as 22.12°P and 13.2%vol,with a fermentation degree of 77.08%;The content of flavor substances in the finished Imperial Stout beer was determined,and the total content of higher alcohols and esters was253.09mg/L and 74.72mg/L,respectively.The alcohol ester ratio was 3.39,which is in line with the category of high-quality alcohol ester ratio and will not cause a "heady" feeling to drinkers.The acetaldehyde content and dimethyl sulfur content in beer are 3.24mg/L and0.04mg/L,respectively,which are below the threshold and will not cause flavor defects in beer.For the characteristic flavor components of Imperial Stout Beer,the content of Maillard heterocyclic compounds mainly composed of maltol,pineapple ketone,2-acetylpyrrole,and2-methylpyrazine is 0.85mg/L,0.53mg/L,0.28mg/L,and 0.14mg/L,respectively,giving Imperial Stout Beer a strong characteristic "malt flavor".The sensory evaluation results of the finished Imperial Stout beer show that its foam is white and delicate,the wine body is full and warm,the taste is mellow,and the malt flavor is in harmony with the alcohol ester flavor.This study provides scientific and theoretical support for the production and brewing of Imperial Stout Beer,and has made significant contributions to the future development of Imperial Stout Beer.