During pretreatment, lignocellulosic material is broken down to smaller sugar units and thus available for enzymatic attack. To date two-step, dilute-acid pretreatment of biomass has shown to result in the highest sugar and ethanol yields in lab-scale. The hemicellulose is hydrolyzed in the first step then solid material and liquid fraction are separated. The solid material is fed to second reactor while the liquid solution is taken to the fermentation of hemicellulose sugars. In an industrial process filtration and washing of material between two steps are still difficult as it should be performed at high pressure to save energy. However, the applied pressure forms more compact solids which might affect the subsequent steps. Therefore, the right choice of separation-technique together with the number of separations has an important impact on structure of the pretreated material and thus final ethanol yield. In the current study, a number of methods for liquid/solid separation between two pretreatment steps and the influence on the digestibility of solids, as sugar yield in the second step or by enzymatic hydrolysis, are under investigation.