To determine the rate of product formation per biomass,
carrier material was taken from the reactor and incubated
anaerobically in wort of 12°P. Incubation occurred at two
different temperatures, 2°C and 12°C. At regular time intervals,
culture samples were taken, filtered over a 0.45 mm
filter, and subsequently frozen. The concentrations of the
different flavor components were determined by headspace
analysis using gas chromatography (GC-HS). To determine
in vivo reducing capacity, similar experiments were performed
in the presence of aldehydes. A stock solution of
3-methylbutanal, hexanal and heptanal in wort was prepared
by sonication as described by Van Iersel et al. [12]. Aldehydes
were added to the cell suspension to a final concentration
of 0.3 mM and concentrations of flavor components
were determined as described below.