Hydrolysates obtained by enzymatic saccharification of wheat straw or cornstover pretreated by steam explosion in classical or acidic conditions, were found non fermentable into acetone-butanol (ABE). A simple treatment involving heating the hydrolysates in the presence of calcium or magnesium compounds such as Ca(OH)2 or MgCO3 at neutral pH values restored normal fermentability to these hydrolysates. The detoxification treatment could be included in the standard neutralization and sterilization procedures performed before fermentation.