Non-food plant biomass is subjected to hot-water extraction in a pressurized vessel at an elevated temperature up to about 250° C. and at a pH below about 7.0, to yield an aqueous extract containing hemicellulosic components, other wood-derived compounds, and a lignocellulosic residue. The separated aqueous extract or liquor is purified and concentrated through a multi-step process producing fermentable sugars. At each stage, inhibitory chemicals such as acetic acid, lignin, and furfural are separated and eventually recovered as commercial chemicals. The lignocellulosic residue may be further processed, as a material with enhanced resistance to sorption of water, for manufacture of improved pulp and paper, construction materials, pellet fuel, and/or other useful products.