Yeast glucose consumption rate and respiratory quotient (RQ).

Under purely respiratory metabolism at low biomass formation (growth) rates, roughly one CO₂ molecule will be produced for each O₂ molecule consumed. Fermentation does not require molecular O₂ as the final electron acceptor, and will only produce one CO₂ in the first decarboxylation step of each pyruvate. Hence, RQ ratios that are significantly greater than one indicate a fermentative activity. All ethanol-forming yeasts have RQ ratios significantly greater than one, while all non-ethanol forming yeasts have an RQ close to, or equal to one. The average glucose consumption rates (left) and RQ ratios (right) between biological replicates are illustrated for cultures at steady-state (SS), time interval 5–20 minutes (Early-phase) and time interval after 60 minutes (Late-phase) while glucose was still present after a glucose pulse. Error bars correspond to the standard deviation.