TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: In the method (M1), the hydrolysis mixture is subsequently subject to fermentation to an ethanol concentration of at least 4 wt.%. The cellulase enzyme activity is recovered after vacuum distillation at a temperature of less than or equal to 60 degrees C. The cellulase activity is recovered from hydrolysis residue remaining after vacuum distillation by a wash at pH 9 or 7-9. The recovered cellulase activity is included in subsequent hydrolysis cycles by using recovered enzyme solution to soak fresh pretreated biomass prior to hydrolysis. The initial cellulase dose is 18 FPU/g DM. In the method (M1), the cellulase preparation used to provide the supplementation dose is different from the cellulase preparation used to provide the initial cellulase dose. In the method (M1), a commercially available cellulase preparation provided by GENENCOR (RTM: biomass enzyme) is used that is optimized for lignocellulosic biomass conversion and that comprises exoglucanases, endoglucanases, hemicellulases, and beta glucosidases and that has endoglucanase activity such that 1 FPU cellulase activity is associated with at least 31 carboxymethylcellulose units (CMC U) endoglucanase activity and that further has beta glucosidase activity such that 1 FPU cellulase activity is associated with at least 7 p-nitrophenylglycerol units (pNPG U) beta glucosidase activity. In the method (M1), a commercially available cellulase preparation provided by GENENCOR is isolated from genetically modified Trichoderma reesei. In the method (M1), a commercially available cellulase preparation provided by GENENCOR had a pH optimum of 5 or within 0.5 pH units of 5. In the method (M1), a commercially available cellulase preparation provided by NOVOZYMES (RTM: biomass enzyme) is used that is optimized for lignocellulosic biomass conversion and that comprises exoglucanases, endoglucanases, hemicellulases, and beta glucosidases and has a pH optimum of 5 or within 0.5 pH units of 5. In the method (M1), a commercially available cellulase preparation provided by NOVOZYMES is used that is optimized for lignocellulosic biomass conversion and that comprises exoglucanases, endoglucanases, hemicellulases, and beta glucosidases and that has beta glucosidase activity such that 1 FPU cellulase activity is associated with at least at least 7 or at least 20 pNPG U beta glucosidase activity. In the method (M2), the wash containing recovered cellulase activity is adjusted to a pH range in which the enzyme is active and used to soak pretreated biomass (preferably wheat straw) prior to enzymatic hydrolysis. In the method (M2), greater than or equal to 70% of the recovered cellulase activity is adsorbed to the soaked biomass. EXAMPLE - No suitable example given.