Study On Enhancing Foam Stability Of Draft Beer

Draft beer has represented the development trend of our country's beer industry. Draft beer has the characteristics of pure taste and full nutrition so that it has become a kind of healthy drink which is popular with customers. But there is an obvious shortage on the stability of draft beer foam, witch means the stability of draft beer foam will draft off along with the delay of store time. The main reason leading to this result maybe the protease A which is produced by beer yeast.In this paper, the examination method of protease A was optimized, which will provide a promise of determine the activity of protease A more accurately. Through discussing the relation between protease A and the stability of beer foam, we have certified that the rudimental living protease A in draft beer is the key factor affecting the stability of beer foam. This study starts with selecting of low-producing proteinse A strains which by using two kinds of chemical mutagen including NTG and EMS treatment of two Saccharomyces cerevisiae. By use factor and orthogonal trial to determine the best filter condition of the acid denaturation of hemoglobin plate and the optimum condition of filter is: the peptone content in glycerine culture medium is 1%, the pH of hemoglobin of acid-denatured is 1, the acid-denatured time of hemoglobin is 1.5h and the hydrolysis temperature is 37℃, through which, reducing blindness of the selection process and improve the efficiency of the breeding. Beer yeast mutant strain NE36 which can product low proteinase A is selected through mutation breeding methods, through evaluating their fermentation performance and the genetic stability prove that they are applicable to industrial production. At last they are used in pilot-test scale and large-scale production, the results showed that the dynamic of protease A produced from mutant NE36 is significantly lower than the starting strain, which reducing the rate at more than 20%.The attenuation of foam stability of large-scale production of finished beer has markedly improved compared with that of the starting strain, so it has a good prospects for industrial applications.