The present invention is directed to a method of pre-treating a lignocellulosic feedstock. The lignocellulosic feedstock comprises cereal straw, stover, or grass. One or more than one bale of lignocellulosic feedstock is conveyed into a pre-treatment reactor. Steam and acid are added to the bales and are maintained at a temperature, acid concentration, and for a time sufficient to hydrolyze hemicellulose to xylose and increase susceptibility of cellulose to digestion by cellulase enzymes, thus producing a pre-treated feedstock. The pre-treated feedstock is then removed from the pre-treatment reactor.