Fig. 1a shows the TV dynamics in the headspace. At the lowest glucose concentration (run 1), the production was faster, attaining a maximum around 28 mmol/l per gram after 40 h, which was maintained at same level for 140 h. At intermediate glucose concentra- tion (run 2), the increase in TV was slower and the maximum (24 mmol/l per gram) was attained after 280 h. This could be due to a decrease in water activity in relation to the high glucose concentration. It could also be partly explained by a catabolic repression due to the carbon source. This phenomenon was amplified at the highest glucose concentration (run 3), where the TV remained very low throughout the experiment. This correlated with the olfactometric observations (Table 1).