Abstract
Wort FAN (free amino nitrogen) is the sum of the individual amino acids and small peptides (mainly di-, tripeptides). A further source of assimilable nitrogen is ammonium ions. This study has substantiated previous reports that both lager and ale yeast strains can simultaneously use wort amino acids and small peptides followed by ammonium ions. It is confirmed that amino acids are taken up in a distinct order. However, it is proposed that methionine, isoleucine and leucine be reclassified from group B to group A. Further studies are necessary to confirm that wort with enhanced L-methionine levels reduced fermentation rate and extent and lower beer VDK levels. Also the reason why fermenting wort containing supplemented lysine levels produced elevated VDK concentrations is unclear, but it is probably due to the enhanced biomass formation compared to the unsupplimented wort. Proteolytic enzymes secreted/excreted by viable yeast cells during fermentation are responsible for degrading larger wort peptides into smaller molecules and provides the yeast with an additional source of assimilable nitrogen and this hydrolysis has a negative effect on beer foam stability.
Published Version
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