Relative amount of free β-glucosidase activity from Cellic® CTec2 with or without addition of pretreated wheat straw in the presence of different concentrations of PEG6000. Substrate loadings: without PWS, 0 mg/mL; with PWS, 48 mg/mL (1.5 w/v-% lignin, composition in Table 1). Total β-glucosidase activity: 500 nkat/mL. The activities are relative to the controls without added substrate. PWS, pretreated wheat straw.