A method of generating a refined sugar stream that comprises xylose from a biomass hydrolysis solution including contacting a biomass hydrolysis solution that includes a population of mixed sugars comprising xylose, an acid, and impurities, with an extraction solvent to form an extraction mixture; and separating from said extraction mixture a first stream that includes the acid and a second, refined sugar stream that includes the extraction solvent and xylose. The extraction solvent is a tri-alkyl phosphine oxide, a dialkylsulfoxide, or a dialkylphosphite, or any combination thereof.