The main carbonyl compounds present in wort are
formed by three different reactions, viz. Maillard reactions
between amino acids and sugars, Strecker degradation of
amino acids, and degradation of lipids [19]. Compounds
formed in the latter two reactions are also intermediates of
metabolic pathways of yeast and may thus be taken up by
the cells and metabolized. In the experiments, it was observed
that reduction of aldehyde on a molar base was
higher than the production of the corresponding alcohol.
This may be explained by metabolization of aldehydes as
precursors for lipid synthesis. The ratio for heptanol/heptanal
was close to one, suggesting that a carbon chain of
seven atoms is less favorably metabolized than six or eight
atoms. This is in line with the observation that the lipids of
yeast cells are composed of fatty acids with an even number
of C-atoms [20].