Biomass of olive tree pruning can be considered a suitable raw material for the production of ethanol due to its high content of potentially fermentable carbohydrates. However its high extractives content could cause condensation reactions between extractives and acid insoluble lignin during pretreatment, hindering the enzymatic hydrolysis of pretreated material. In this work, the effect of extractives removal before steam explosion of olive tree pruning was evaluated. The objectives are to recover as much glucose as possible in the extraction stage and to avoid the condensation reactions. The effect of temperature and time of water extracted material on sugars recovery was studied using a response surface method according to a central composite design. Extractive removal previous to steam explosion resulted in 20% more total sugars recovery in comparison to a material without water extraction stage. (C) 2011 Elsevier Ltd. All rights reserved.