Barley straw is nowadays being considered a potential lignocellulosic raw material for fuel-ethanol production as an alternative to starch-or sugar-containing feedstock. In this work, several configuration strategies for ethanol production from steam-exploded barley straw by Kluyveromyces marxianus CECT 10875 have been studied with the aim of obtaining higher ethanol concentrations. Different substrate loading (2-15%, w/v) were studied during enzymatic hydrolysis. The xylanase contribution on glucose production and glucan conversion at different substrate loading was also investigated. In addition, three different process configurations, separate hydrolysis and fermentation, simultaneous saccharification and fermentation and presaccharification and simultaneous saccharification, were compared at different water insoluble solids concentration (5%, 10% and 15%). The influence of xylanase addition on the ethanol yield was studied as well. Results show that endo-xylanases improved glucan conversion and ethanol yield compared with a standard enzymatic mixture, markedly at low substrate concentration. The positive effect of added xylanase was most evident at early stages of enzymatic hydrolysis. Regarding process configurations for the period of 72 h, SSF with endo-xylanases provided the best ethanol yield, nearly 70%, for 10% WIS. Nonetheless, the higher ethanol concentration, 29.4 g/l, was obtained at 15% WIS. (C) 2010 Elsevier Ltd. All rights reserved.