Methods and systems for pretreating lignocellulosic biomass are disclosed. An acid solution between 1% to 1.6% sulfuric acid is applied to the biomass. The biomass is subjected to an elevated temperature to cause the production of xylose, glucose, and furfural. Adjustments to temperature, acid concentration, and time can generate at least 80% or 90% of theoretical xylose, 45% or 50% of the theoretical glucose, and less than 4000 ppm of furfural in the xylose liquor. A portion of the resulting xylose liquor may be separated from the glucan solids. The xylose liquor, still highly acidic, can be recycled to reduce subsequent acid loading requirements. Makeup acid solution is added to the xylose liquor and subsequent biomass to ensure a proper solids to liquids ratio. The biomass is again treated to higher temperatures to yield sugars. The process may be repeated for each subsequent cycle.