NOVELTY - Making a biomass hydrolysate, involves catalytically reacting water and a water-soluble C2+O1+ oxygenated hydrocarbon in a liquid or vapor phase with H2 in the presence of a deoxygenation catalyst at a deoxygenation temperature and deoxygenation pressure to produce a biomass processing solvent comprising a C2+O1-3 hydrocarbon in a reaction stream, and reacting the biomass processing solvent with a biomass component, hydrogen and a deconstruction catalyst at a deconstruction temperature and a deconstruction pressure to produce a biomass hydrolysate.    USE - For producing biomass hydrolysate (claimed) which is used in bioreforming processes such as aqueous-phase reforming (APR) and hydrodeoxygenation (HDO).    ADVANTAGE - The method is cost-effective; provides biomass hydrolysate having lower molecular weight oxygenated hydrocarbon; and reduces biomass deconstruction costs by avoiding the need to purchase expensive deconstruction solvents and by avoiding solvent recovery and clean-up costs by recycling solvent from intermediates produced in bioreforming processes. The deconstruction catalyst used in the method can be recycled for re-use in upstream processes.    DETAILED DESCRIPTION - Making a biomass hydrolysate, either involves method (M1): catalytically reacting water and a water-soluble C2+O1+ oxygenated hydrocarbon in a liquid or vapor phase with H2 in the presence of a deoxygenation catalyst at a deoxygenation temperature and deoxygenation pressure to produce a biomass processing solvent comprising a C2+O1-3 hydrocarbon in a reaction stream, and reacting the biomass processing solvent with a biomass component, hydrogen and a deconstruction catalyst at a deconstruction temperature and a deconstruction pressure to produce a biomass hydrolysate (Q1) comprising at least one member selected from water-soluble lignocellulose derivative, water-soluble cellulose derivative, water-soluble hemicellulose derivative, carbohydrate, starch, monosaccharide, disaccharide, polysaccharide, sugar, sugar alcohol, an alditol and polyol; or method (M2): catalytically reacting water and a water-soluble C2+O1+ oxygenated hydrocarbon in a liquid or vapor phase with H2 in the presence of a deoxygenation catalyst at a deoxygenation temperature and deoxygenation pressure to produce an oxygenate comprising a C2+O1-3 hydrocarbon in a reaction stream, catalytically reacting in the liquid or vapor phase the oxygenate in the presence of a condensation catalyst at a condensation temperature and condensation pressure to produce a biomass processing solvent comprising at least one C4+ compounds, and reacting the biomass processing solvent with a biomass component, hydrogen and a deconstruction catalyst at a deconstruction temperature and a deconstruction pressure to produce the biomass hydrolysate (Q1). An INDEPENDENT CLAIM is included for deconstructing (M3) biomass, involving reacting a biomass slurry with a biomass processing solvent comprising a C2+O1-3 hydrocarbon at a deconstruction temperature of 80-350 degrees C and a deconstruction pressure of 100-2000 psi to produce the biomass hydrolysate (Q1), where the biomass processing solvent is produced by catalytically reacting in the liquid or vapor phase an aqueous feedstock solution comprising water and a water-soluble oxygenated hydrocarbons having C2+O1+ hydrocarbon with H2 in the presence of a deoxygenation catalyst at a deoxygenation temperature and deoxygenation pressure.