High-yielding method for chemical hydrolysis of lignocellulose into monosaccharides. The process of the invention can additionally be applied to cellulose, xylan and related biomass polysaccharides, such as galactan, mannan, or arabinan. The method is employed for hydrolysis of a biomass polysaccharide substrate. The process is carried out in an ionic liquid in which cellulose is soluble in the presence of catalytic acid at a temperature sufficiently high to initiate hydrolysis. Water is added to the reaction mixture after initiation of hydrolysis at a rate controlled to avoid precipitation yet avoid undesired sugar dehydration products such ad HMF. Hydrolysis product is useful as feedstock for fermentations including fermentation processes for ethanol, butanol and other fuels.
