Hot compressed liquid water Was used to treat switchgrass in a method called hydrothermolysis to disrupt lignin, dissolve hemicellulose, and increase accessibility of cellulose to cellulase. Three temperatures (190, 200, and 210 degrees C) and hold times (10, 15, and 20 min) were tested. Switchgrass treated at 190 degrees C for 10 min had the greatest xylan recovery in the prehydrolyzate. Less than 0.65 g/L glucose were released into the prehydrolyzate for all pretreatment conditions, indicating most glucose was retained as Cellulose in the solid Substrate. 5-Hydroxymethylfurfural (HMF) and furfural formation in the prehydrolyzate were found to be less than 1 g/L for all treatments. The highest concentration of ethanol, 16.8 g/L (72% of theoretical), was produced from switchgrass pretreated at 210 degrees C and 15 min using simultaneous saccharification and fermentation (SSF) at 45 degrees C with the thermotolerant yeast Kluyveromyces marxianus IMB4 and 15 FPU cellulase/g glucan. (C) 2009 Elsevier Ltd. All rights reserved.