Study On Brewing And Oak Aging Technology Of Imperial Stout

In small scale,to study the brewing process conditions of Imperial Stout,and optimize the brewing process conditions by single factor experiment combined with response surface experiment.It analyzed mainly for the three factors that the original wort concentration,fermentation temperature,and the additive contents of white granulated sugar when in the secondary fermentation.And determined on the optimal brewing process conditions:the fermentation temperature of 20±0.5℃,the original wort concentration of 16 ~oP,the white granulated sugar added of 5.1%.The above optimized Imperial Stout is mainly based on the aroma that alcohol flavor,which is fruit flavor and rose-like flavor,accompanied by strong alcohol flavor and malt flavor;mellow taste with strong impact and layer sense;the foam is fine and brown;the overall taste is harmonious,complex and changeable;the flavor malt and inter action of alcohol flavor with a strong sense of hierarchy.The optimized Imperial Stout was used for the aging process experiment(this thesis mainly studied the aging process by oak slices).According to the influence of the producing area and baking degree of the oak slices,we selected oak slices with the medium and moderate of baking degree.It mainly included mocha oak slices,vanilla oak slices,cognac oak slices and butter bread oak slices.We detected the flavor substances of the beer by GC-MS and combined with the threshold value to optimized the aging process with response surface experiment,the following conclusions is drawn:(1)The conditions of aging process:the Imperial Stout with mocha flavor aging time of 45 days,the additive contents of oak slices is 5.2g/L,the aging temperature of 0±0.5℃;Imperial Stout with cognac flavor aging time of 30 days,the additive contents of oak slices is 6.1g/L,the aging temperature of 0±0.5℃;the Imperial Stout with vanilla flavor aging time of 60 days,the additive contents of oak slices is5.1g/L,the aging temperature of 0±0.5℃;the Imperial Stout with bread and butter flavor aging time of 75 days,the additive contents of oak slices is 5.7g/L,the aging temperature of 0±0.5℃;the Imperial Stout that under the aging process condition with oak barrel aging style,and provides a theoretical support for the aging process through the concrete analysis to flavor compounds.(2)The mocha and vanilla oak slices come from American;the cognac,bread and butter oak slices come from France,check the flavor compounds by GC-MS,analysis the kinds of flavor compounds and contrast the content of flavor compounds,combine with the sensory evaluation,which found that the content and the kinds of flavor compounds in oak slices from American are more than France,but the oak slices from France more delicate.(3)The kinds of flavor compounds:there are 79 kinds of flavor compounds in the Imperial Stout with mocha flavor;there are 76 kinds of flavor compounds in the Imperial Stout with vanilla flavor;there are 71 kinds of flavor compounds in the Imperial Stout with cognac flavor;there are 72 kinds of flavor compounds in the Imperial Stout with bread and butter flavor;and the oak slices from American have more flavor compounds than oak slices from France at the same degree of roasting.(4)During the aging time,monitored the main physical and chemical indexes and analysis the change trend of it,and it was found that total acid and chroma increased with the increase of aging time,while alcohol and bitter decreased with the increase of aging time.