Metabolism of nitrogenous wort components by brewers' yeast
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A quantitative and qualitative identification of the nitrogenous constituents of unfermented and final fermented wort has been performed for five industrial yeast strains. Results highlight the importance of three key amino acids in yeast fermentation performance. Supplementation of wort using individual amino acids and ammonia clearly demonstrate lysine and arginine to be marker nitrogen wort constituents. Synergistic effects of individual wort free amino acids and ammonia on yeast fermentation efficiency were also examined. Further analysis of nitrogeneous wort constituents included examination of oligopeptides with a molecular weight of less than 500 Daltons and the influence of yeast proteases on the availability of small peptides during fermentation. Both lager and ale yeast can simultaneously use amino acids and small peptides as sources of assimilable nitrogen. Laboratory malt and mash analysis of 28 malt types revealed that 80-95% of total free amino nitrogen originates during malting and the remaining 5-20% during mashing.