TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Process: In the step of providing (step a), the feedstock is agricultural waste, grass, forestry biomass, sugar processing residues, or their combinations. The agricultural waste is corn stover, soybean stover, corncobs, rice straw, rice hulls, corn fiber, wheat straw, barley straw, canola straw, oat straw, oat hulls, or their combinations. The grass is switch grass, miscanthus, cord grass, rye grass, reed canary grass, or their combinations.The forestry biomass is recycled wood pulp fiber, softwood, hardwood, sawdust, or their combinations. The sugar-processing residue is bagasse, beet pulp or their combinations. In the step of providing (step a), the feedstock is slurried in an aqueous solution. In the step of pumping (step b), the heating train comprises 2-8 heating stages. The step of cooling (step e) comprises 2-8 flashing stages. The slurry is subsequently cooled to 30-100degreesC after the final flashing stage.In the step of adding (step c), the acid is sulfuric acid, sulfurous acid, or sulfur dioxide. In the step of adding (step c), the acid is added to the feedstock slurry prior to the heating train. In the step of adding (step c), the acid is added to the feedstock slurry after the heating train. In the step of adding (step c), the acid is added to the feedstock slurry in a heating stage. After the step of adding (step c) and before the step of pumping (step d), the feedstock slurry is reacted at a temperature of less than 170degreesC in the presence of 0.5-3% weight of acid on weight of initial feedstock to hydrolyze the hemicellulose. After the step of cooling (step e), the slurry is submitted to enzymatic hydrolysis by cellulase enzymes.In the step of pumping (step b), live steam is added to one or more than one heating stage to heat the feedstock slurry. In the step of using steam energy (step f), flash steam, or its portion, from at least one of the two or more flashing stages is used to heat a stream of water, steam, or their combination, and where at least a portion of the heated stream is sent to the heating train to heat the feedstock slurry. EXAMPLE - No relevant example given.