A process for producing a pretreated feedstock is provided. The feedstock is selected from grasses, cereal straws, stover, and combinations thereof, and least about 80% of the feedstock has a particle length of between about 2 cm and about 40 cm. This process comprises wetting the feedstock in liquid, pressing the wet feedstock through one roll press or a series of roll presses to remove at least a portion of water and soluble substances from the wetted feedstock and to shear the feedstock to produce feedstock particles of a size suitable for pumping at a solids concentration of about 8% to about 20% when slurried. At least one roll press, or at least one roll press in the series of roll presses comprises rolls with circumferential v-shaped grooves. The pressed feedstock particles are slurried to produce a slurried feedstock having a consistency of between about 8% and about 20%, and the slurried feedstock pumped into a pretreatment reactor. Dilute acid pretreatment of the slurried feedstock is carried out at a temperature of 160° C. to 280° C.