In the production of cellulose ethanol, lignocellulosic biomass can be pretreated by enzymatic hydrolysis to breakdown the cellulose molecules into sugars for ethanol.fermentation. The conversion of cellulose to sugars involves the reduction of the solid biomass by grinding, followed by the addition of cellulose-degrading enzymes (cellulases) in a reaction system. When there are "no significant amounts of free liquid water present" in the reaction system (roughly 20% solids content or higher), the process becomes a system for "high solids enzymatic hydrolysis". The potential advantage of high solids enzymatic hydrolysis reduce operating cost resulting from: (1) larger reaction capacities, (2) lower energy requirements for the distillation of ethanol, and (3) lower volumes of wastewater to be treated. However, the process may also result in lower sugar yields resulting from higher concentrations of inhibitory end products and insufficient mixing. Scientists from the University of Copenhagen (Denmark) studied the factors which determine the over-all sugar yields in the high solids enzymatic hydrolysis of cellulosic biomass. Their studies showed that a dominant cause for decreased sugar yields is the inhibition of cellulase adsorption into cellulose by the hydrolysis products. "Product inhibition by glucose and in particular cellobiose (and ethanol in simultaneous saccharification and fermentation) at the increased concentrations at high solids loading plays a role but could not completely account for the decreasing conversion". The presence of inhibitors (lignin-derived or hemicellulose-derived inhibitors), as well as insufficient mixing, are not seen as primary factors for decreased sugar yields. The paper appears in the open access journal, Biotechnology for Biofuels (URL above)..