Methods and systems for fractionating lignocellulosic biomass including hemicellulose, cellulose and lignin, including exploding the biomass cells to devolatilize the biomass, hydrolyzing the hemicellulose to produce a liquid component including hemicellulosic sugars and a solid component including less than 10% hemicellulose, separating the liquid and solid components, vaporizing the cellulose in the solid component, and condensing the cellulosic sugar vapors. The methods and systems may vaporize the cellulose in a continuous steam reactor at a temperature of about 400-550° C. and a pressure of about 1-3 bara. Electromagnetic and/or electroacoustic treatment such as ultrasound and/or microwave treatment may be applied to the biomass immediately before or during cellulose hydrolysis.