The Research Of Brewing Technology And The Analysis Of Flavor Compounds On Watermelon Craft Beer

Preparation technology of beer yeast s189(Saccharomyces cerevisiae) seed used for watermelon craft beer is studied. In order to achieve higher density of s189 yeast, the components of wort medium are optimized with the method of response surface and the effects of culture conditions on the growth of beer yeast s189 are explored in the paper. First, the three major factors greatly impacting on the growth of beer yeast s189 are defined with the method of single factor experiment. They are reducing sugars, magnesium sulfate and potassium dihydrogen phosphate respectively, and their approximate range are defined. Then the optimal concentration of three factors is determined through the central composite design experiments and the response surface analysis: sugar 85 g/L, magnesium sulfate 1.2 g/L, and potassium dihydrogen phosphate 0.85 g/L. Finally, the largest OD600 of beer yeast s189 from the optimized growth medium reaches 16.03, which is close to 15.88, the maximum value of the model one.The fermentation process of watermelon craft beer is incorporated into the study. Watermelon craft beer is developed with the unique low temperature fermentation process of beer using watermelon juice and brewers' barley malt as the main material for brewery. The addition ratio and adding time of watermelon juice and the influence of the original wort concentration to watermelon beer quality are studied with a series of methods including the single factor test, response surface analysis, sensory analysis and the physical and chemical indicators. The optimized fermentation conditions are determined as follows: watermelon juice 14%, watermelon juice adding time 4.5 days in the main fermentation, the original wort concentration 11.2 oP. Under this condition, 400 L fermentation experiment is carried out and then a watermelon beer with typical flavor of beer and watermelon is obtained.Flavor substances of watermelon craft beer and the corresponding ordinary craft beer are analyzed on the preliminary scale. In order to study the watermelon craft beer flavor substances, solid-phase micro-extraction(HS-SPME) is applied, combining with the method of gas chromatography-mass spectrometry(GC-MS). Watermelon craft beer and the corresponding ordinary craft beer flavor substances make a comparative analysis possible. And ultimately, 48 kinds of substances are isolated from watermelon craft beer, among which 36 substances are identified. 42 kinds of substances from the corresponding ordinary craft beer are isolated, among which 41 substances are identified. After analysis, main flavor substances of watermelon craft beer are octanoate, isoamyl acetate, ethyl decanoate, n-hexyl acetate, ethyl acetate, benzene, esters such as decanoate substance; main flavor substances of the corresponding ordinary craft beer are octanoate, isoamyl acetate, ethyl decanoate, ethyl acetate, benzene, acid, etc. Compared with the corresponding ordinary craft beer, some unique flavor substances of watermelon craft beer mainly are ethyl caproate, decanal, aldehyde Cocker, azelaic acid ethyl ester, and esters such as decanoate aldehydes.