Microaeration (injecting air into the headspace) improved the fermentation of hemicellulose hydrolysates obtained from the phosphoric acid pretreatment of sugarcane bagasse at 170 degrees C for 10 min. In addition, with 10% slurries of phosphoric acid pretreated bagasse (180 degrees C, 10 min), air injection into the headspace promoted xylose utilization and increased ethanol yields from 0.16 to 0.20 g ethanol/g bagasse dry weight using a liquefaction plus simultaneous saccharification and co-fermentation process (L+SScF). This process was scaled up to 801 using slurries of acid pretreated bagasse (96 h incubation; 0.6 L of air/min into the headspace) with ethanol yields of 312-347 L (82-92 gal) per tonne (dry matter), corresponding to 0.25 and 0.27 g/g bagasse (dry weight). Injection of small amounts of air into the headspace may provide a convenient alternative to subsurface sparging that avoids problems of foaming, sparger hygiene, flotation of particulates, and phase separation. (C) 2011 Elsevier Ltd. All rights reserved.