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.degree. C. to
280.degree. C.