Research On The Characteristic Flavor Substances Of Top-fermented Wheat Beer

The top-fermented wheat beer is deeply liked by consumers for its distinctiveclove-like aroma. In this study, its characteristic flavor substances—4-vinylguaiacol(4VG) and4-vinylphenol (4VP), ethyl acetate and isoamyl acetate were made anintensive research. The brewing process parameters of wheat malt proportion,mashing-in temperature, boiling time, pitching rate, fermentation temperature andstorage time were studied by a pilot-scale brewing test of2tons. The brewing processcontrol of the four typical flavor substances were proposed by the pilot-scaleexperiment in combination with chromatography analysis and sensory evaluation ofbeer. The flavour and product quality of wheat beer was improved.The main compounds of constituting the overall characteristic flavor of beer areethyl acetate and isoamyl acetate. They impart fruit aroma to beer and make the flavorof beer more harmonious.4VG and4VP are the necessary components of clove-likearoma as the most active volatile phenols in top-fermented wheat beer. They also arethe indispensible characteristic component in the comprehensive evaluation of wheatbeer flavor. The amount of the presence of the four characteristic flavor substancesplays an important role in the style and quality of the wheat beer. They will make theflavor unpleasant and the taste rough when their contents in beer are too high.Therefore, in this paper the content of four characteristic flavor compounds intop-fermented wheat beer were achieved the best by optimizing the brewing processaccording to the formation mechanism and influencing factors.In this paper, the detection method of4VG and4VP was developed and optimizedby using the high performance liquid chromatography in our laboratory at present. UVspectrophotometer was used to determine the best absorption wavelength of4VG and4VP at260nm. The best composition of the mobile phase was determined as follows:methanol/ultrapure water/phosphoric acid=400:590:10. The retention time of4VGand4VP was27min and25min respectively. Full separation of the two volatile phenolswas achieved on this condition. The accuracy of this detection method was higher, andthe cost was lower. Therefore, this method can be used as an effective means todetermine4VG and4VP.The influence of wheat malt proportion, mashing-in temperature and boiling timeon4VG and4VP, as well as pitching rate, fermentation temperature and storage timeon ethyl acetate and isoamyl acetate were studied by a pilot-scale brewing test of2 tons respectively. The brewing process was optimized using response surfacemethodology. Based on the response surface, the optimum acceptability of4VG and4VP processing parameters were: wheat malt proportion40%, mashing-in temperature44.11℃, boiling time91.75min. Under this condition, the total content of4VG and4VP was3.9126mg/L. The best brewing process parameters of ethyl acetate andisoamyl acetate were also determined as follows: pitching rate3.95%, fermentationtemperature18.45℃, storage time5.1d. The total amount of ethyl acetate and isoamylacetate was46.968mg/L on this process condition. A brewing experiment whichintegrated the two optimum process conditions was performed. The physicochemicalindexes and sensory evaluation of top-fermented wheat beer was good.