Effect of aeration on tSSF. A) 24 hour activity of samples drawn from 80 g/L Avicel tSSF (panel B) and transferred to either nitrogen or air-filled serum bottles at 0, 24, 48 and 72 hours, normalized to 0–24 hour production under respective conditions. B) Sugar and ethanol concentrations from an 80 g/L Avicel tSSF. C) Total sugar (cellobiose plus glucose) and ethanol concentrations measured in air-filled serum bottles after sampling from tSSF. Ethanol (E, triangles) and sugar (S, circles) from samples transferred at 0 (filled), 24 (open), 48 (shaded), and 72 (diagonal cross) hours. D) Ethanol concentrations produced in samples from tSSF transferred to nitrogen-filled serum bottles. Overall, the introduction of air to tSSF samples slowed the rate of cellulase inactivation compared to samples maintained under anaerobic conditions. Error bars indicate standard error between replicate bottles.