Methods for producing ethanol from cellulosic biomass and, in particular, methods for controlling steam explosion pretreatment operations are disclosed. Biomass is discharged from a plug screw feeder into a pretreatment digester. The total solids content of biomass entering the pretreatment digester is calculated to provide operational data and feedback control to adjust some parameters (open drain openings, force exerted by the damper, rotational speed of the plug screw feeder; total solids content of the biomass introduced into the feeder) of the plug screw feeder