The Content of Some Organic Acids in Beer and Other Fermented Media

The acid content of a range of ales and lagers has been measured for some organic acids related to the Krebs cycle, and found to vary widely. Acetate, pyruvate, lactate, succinate, pyroglutamate, malate and citrate were present in all cases and α-ketoglutarate was usually detected. α-Hydroxyglutarate was recognized in a number of beers. The effect of the acids on the pH of beer is assessed. The strain of yeast which is used markedly influences the levels of all acids except pyroglutamate and the conditions of yeast propagation have a substantial influence on the extent of acid accumulation. During the fermentation of wort and synthetic media the extent of organic acid excretion is proportional to the extent of fermentation, but the nature of the acids which are excreted varies during the fermentation period. In synthetic media, nitrogen source is shown to have a substantial effect on the accumulation of organic acid. Pyruvate and acetate levels vary inversely towards the end of fermentation, suggesting that yeast converts pyruvate to acetate.