Evidence of Strecker aldehyde excretion by yeast in cold contact fermentations.

A medium containing labeled leucine-d(10) has been used to show that Saccharomyces cerevisiae was able to produce deuterated 3-methylbutanal in a cold contact fermentation. Whereas residual unreduced Strecker aldehydes bound to polyphenols were considered until now as the main defect of alcohol-free beers, yeast emerges from this work as an additional source of worty flavor. When the same experiment was conducted without leucine, 3-methylbutanal excretion also occurred, indicating that valine could be used by yeast as precursor.