Changes in Organic Acids during Beer Fermentation

The profiles of seven kinds of organic acids (citric acid, malic acid, fumaric acid, succinic acid, lactic acid, formic acid, and acetic acid) of worts made from different proportions of rice adjuncts and corresponding beers were analyzed, and the changes in these organic acids during beer fermentation were studied. Results showed that rice proportions had a huge effect on the profiles of organic acids of wort and beer. The total content of these seven organic acids in the cooked rice mash was less than one-fifth of that in the all-malt wort when the extract was the same. The major organic acid in the cooked rice mash was acetic acid, which constituted about 40% of the total organic acids. The abundant organic acids in worts except for the cooked rice mash were citric acid, malic acid, lactic acid, and acetic acid, but the contents of fumaric acid and succinic acid were low. In comparison with the corresponding wort, the content of organic acids in beer obviously increased after fermentation, mainly owing to the excretion of succinic acid, acetic acid, and lactic acid. According to the change characteristics of organic acids during fermentation and their initial levels in wort, these seven organic acids were classified into three groups, namely, groups A, B, and C. Citric acid, malic acid, fumaric acid, and formic acid belonged to group A, for which excretion quantity was little during fermentation. Group B comprised lactic acid and acetic acid; the initial contents of these two organic acids were not low, and they were greatly formed during fermentation. Group C just had succinic acid, for which initial concentration in wort was low, but it was largely formed during fermentation.