The Study On Selecting Yeast For Fermenting Ya Pear Wine

Using the culture medium of bean sprout juice agar, 195 strains were isolated from all kinds of fruits and their skins, which were sold in markets in baoding city. After selecting by four grades, two strains, which were suited to fermenting Ya pear wine, were got, named GY1 and GY2, the former from Ya pears and the latter from Mihou peachs. Both of the two strains, identified as Saccharomyces cerevisiae were not poisonous to human being and could be applied to the production of Ya pear wine. Both of the two yeasts could endure the alcohol concentration of 15%, the pH value of 0.98 and the SO2 concentration of 375mg/L. In the other hand, they could ferment in the sugar concentration of 35% normally, and still start to ferment in the sugar of 70%. So they are potential.The properties of fermentation of the three strains, GY1, GY2 and Angle were studied. Conclusions were made that at temperature of 25℃, the properties of GYi and GY2, were better than those of Angle. The logarithmic stage of the two yeasts was one day, which was one day shorter than that of Angel; and the steady stage was 3 days, while that of Angel was not significantly. And both of the properties of enduring SO2 were good, but they were not same completely. The fermenting period of GYi had little anything to do with the content of SO2 (100mg/L~150mg/L), and the fermenting period of GY2 had little anything to do with the lower content of SO2 (50mg/L~100mg/L). That will be useful in improving other species in future. Sensory evaluation tested that two kinds of wine fermented by GYi and GY2 in 25℃ were better than the wine by Angle. Results by Gas Chromatographs tested that the contents of the major favor substances (ethylformate, ethylacetate, isoamyl acetate and ethyl hexanoate) in the Ya pears wine fermented by GYi and GY2 were higher than those by angel; what's more, the content of methanol of the two kinds of wines were 76. 7 X 10-6 g/L and 93. 4 X 10-6 g/L respectively, which were accordant with GB, which regulated that the content of methanol in wine couldn't exceed 0. 8g/L in wine.Optimum fermentation parameters of brewing processing by the two strains were gained by orthogonal test. It was proved that the proper parameters of the two strains were as same as following: fermentation temperature, 25℃; addition of yeast, IX 107cell/mL; primitive pH value, 4. By using the above conditions, the Ya pear wine by GY1 and GY2 were better than the wines by angel and the yeast stored by the lab.