The carbonyl compounds found in pito were
acetaldehyde, benzaldehyde and isobutyraldehyde.
Acetaldehyde is the immediate precursor of
ethanol and formed during the early to mid stages
of fermentation and thereafter it declines to a low
level. It was identified in all samples except 48-
hour mixed culture fermentation. Isobutyraldehyde
was not found in the mixed culture sample after 24
hours. Benzaldehyde was not found in 72 and 48
hours of fermentation with single and mixed cultures
respectively. Some of these compounds have been
reported by Demuyakor and Ohta (1993) to be
present in pito. The effects of aldehydes on finished
beer are a grassy aroma and a papery taste. As a
group, these generally make a negative contribution
to beer flavor and aroma (Briggs et al., 2004). The
principal causes of high acetaldehyde concentrations
in beer as indicated by Geiger and Piendl (1976) are
the use of poor quality pitching yeast, excessive wort
oxygenation, unduly high fermentation temperature
and excessive pitching rates.