Studies On Improvement Of Beer Flavour Stability By Metabolic Control

In the paper, determination of beer real fermentation degree, screen of beer yeast parent strains, mutation of moderately producing SO2 strain as well as beer flavor stability were studied.A method, suitable for the use in the lab, with less beer samples and shorter time was studied to determine alcohol degree and real fermentation degree simply and accurately in beer fermentation.Beer yeasts (Saccharomyces cerevisiae) BY-1-BY-6 were employed for tests. The fermentation characteristics were determined, as well as the production of 862, H2S and diacetyl which effect the beer flavor. Beer yeast BY-1 with better flocculation ability, medium fermentation degree, faster fermentation velocity and higher concentration of SO2 was selected as parent strain.After UV treatment, lead acetate media plates and different differential medium plates containing different sulfur sources were used as primary screening plates. 111 strains, which were white or light brown when grew on the lead acetate media plates, were selected. Then, the different differential medium plates containing NaiS and as the only sulfur sources were used to select 24 strains, which grew well onplates, but didn't grow well on Na2SO3 plates. After compound screening, 10 strains, which had the obviously increased production of SO2 and the decreased production of H2S accordingly, were selected. Mutant M24 was finally selected as the optimal strain after the determination of the fermentation characteristics. When strain M24 was used, the production of 862 was 29.52mg/L, increased by 15.27mg/L; the production of H2S and the peak value of diacetyl were 0.33mg/L and 0.62mg/L, decreased by 45% and 27.9%, respectively.Comparing with BY-1, the result of beer fermentation by M24 indicated that in terms of beer flavor compounds, the concentration of fusel oil decreased obviously with other flavor compounds changing a little. Also, the TBA value of the beer fermented by M24 decreased by 4.8% and the RSV value increased by 35.35%, which showed that the beer flavor stability was improved.