Acetic acid was investigated as a catalyst in steam pretreatment of corn stover. The purpose was to study ethanol production using either baker's yeast or a genetically modified pentose-fermenting version of Saccharomyces cerevisiae, KE6-12. Biogas production was investigated as an alternative for utilization of xylose. The high levels of acetic acid was found to be toxic using KE6-12. Some pentose fermentation was achieved, but the ethanol end concentration was almost the same as using baker's yeast (28 g L-1 compared to 27 g L-1). Using xylose for biogas production resulted in a high total energy recovery. The highest total energy recovery in the products, i.e. ethanol, methane and solids, obtained was 88% compared with the energy in ingoing raw material. This result was achieved when the solids and the liquid was separated after pretreatment. (C) 2014 Elsevier Ltd. All rights reserved.