Factors Influencing The Sour Taste Of Beer

Organic acids are one of important substances,which influence on the sour taste of beer, different organic acid has its unique sourness. The important organic acids were determined by measurement of the thresholds of nine organic(acetic acid, lactic acid, citric acid, malic acid, pyruvic acid, succinic acid, fumaric acid, tartaric acid and oxalic acid) in light beer. The effect of different material proportions and different yeast strain on organic acids were investigated, and study on the change of organic acids in process of beer fermentation. By comparison, the optimal material proportion scheme and yeast strain were chosen. The main conclusions were as following:1.The group threshold of malic acid in control beer had the hightest value in the 9 organic acids,followed by fumaric,lactic,citric,pyruvic,succinic,acetic,oxalic and tartaric acid in sequence. The group thresholds of nine organic acids in degassed beer followed by pyruvic,lactic,acetic,fumaric,succinic,malic,tartaric,oxalic and citric acid in sequence.Besides, we have found that the significant difference in the group thresholds of nine organic acids between degassed and control beers.Triprotic acid has more significant difference than other acids, monoprotic acid was smallest among these acids, while binary acid lie in the middle.2. The thresholds of organic acids in various beer are different, the group thresholds of acetic acid and succinic acid have small difference in two kinds of beers, the difference of citric acid are obvious. We found that the thresholds of organic acids are not low in light beer, such as the thresholds of acetic acid and citric acid in light beer are higher than Tsingtao beer.3. The composition of organic acids in beer depended on raw material of brewing at great extent. Result showed that the contents of citric acid and succinic acid in beer were greatly influenced by material proportion. With measured of the organic acids contents in wort and fermented liquid, the optimal material proportion scheme was considered as: 60%Tradition malt and 40% rice. Four kinds of malt could be ranked and compared by the organic acid contents in fermented liquid and sensory evaluation, the sequence is Tradition malt>Baodai malt>Lacey malt>Stellar malt.4. Yeast strain play an important role on the organic acid contents in the beer. The change of organic acids in process of beer fermentation were studied, and compare four yeast strains' ability which produce the organic acids, it turns out that the contents of most organic acids are increase with fermentation process, the great discrepancy in content of acetic acid among four yeast strains was indeed presented, by contrast, the contents of citric acid,pyruvic acid,fumaric acid and oxalic acid have a little difference.The contents of acetic acid,lactic acid and succinic acid produced by Yeast strain HE are lower than other yeast strains, the contents were 73.1mg/L,107.9 mg/L and 179.4 mg/L,respectively. The content of citric acid is 195.4mg/L, which is relatively high and good for the sour taste of beer.5. In order to obtain the fine brewer's yeast strain, Saccharomyces cerevisiae strain HE was treated with ethyl methane sulfonate (EMS), the mono-colonies growing on wort plate ager containing diacetyl 135μg/mL were isolate. The anti-diacetyl mutants were fermented in 500mL flask with 300mL 10°Bx wort at 12℃for 8 days and selected with the fermented degree and the content of diacetyl,acetic acid,acetaldehyde and total higher alcohols of the fermented liquid as the main target.As a result, the fine strainHE-14 was obtained. The fermented degree of mutant HE-14 was 67.5%, the content of diacetyl, acetic acid,acetaldehyde and total higher alcohols in the fermented liquid were respectively 0.097mg/L,74.3mg/L,4.57mg/L and 87.1mg/L under the conditions of 100 L fermentor with 100L 10°Bx wort at 12℃for 14 days. The fermentated properties of the mutant HE-14 were relatively stable, the sensory evaluation of the beer produced by the mutant strain HE-14 was nice. StrainHE-14 is of well applied prospect on the beer brewing.