Membrane separations can be integrated into a biorefinery to reduce water and energy consumption. Unfortunately, current membrane materials suffer from severe fouling, which limits their applicability. Here, using analytical characterizations along with fouling models, we correlate membrane properties with performance metrics to provide a framework for optimal membrane selection during solid-liquid clarification of a biomass hydrolysate. Five membranes were evaluated: polyether sulfone, mixed cellulose esters, and three surface modified membranes with weak acid, strong acid, and weak base functionalities. Lignin was the primary component responsible for flux decline, due to physical entrapment and chemical adsorption. The best membrane performance (high and sustained flux, low fouling, and high separation factor) was correlated with higher surface roughness, lower hydrophobicity, neutral or positively charged zeta potential, and a larger number of smaller surface pores. These analyses provide valuable information for designing new materials for biorefining processes to reduce fouling and increase stability. (c) 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1246-1254, 2013