NOVELTY - Sugars are produced from biomass by adding biomass to 1st liquid at hydration temperature to produce hydrated biomass, mechanically reducing size of hydrated biomass to produce mixture of size-reduced solid particles, heating mixture of size-reduced solid particles at 1st hydrolysis temperature for 1st hydrolysis time to produce 1st liquid fraction containing sugars having carbon number of 5 and 1st solid fraction, heating 1st solid fraction in acidic medium containing acid at 2nd hydrolysis temperature for 2nd hydrolysis time to produce mixture, and hydrolyzing mixture.    USE - Production of sugars from biomass (claimed).    ADVANTAGE - Inhibitor formation is suppressed, and enzyme load during enzymatic hydrolysis is reduced, decreasing the yield of undesirable products during pretreatment.    DETAILED DESCRIPTION - Sugars are produced from biomass by adding biomass to 1st liquid at hydration temperature to produce hydrated biomass, mechanically reducing size of hydrated biomass to produce mixture of size-reduced solid particles, heating mixture of size-reduced solid particles at 1st hydrolysis temperature for 1st hydrolysis time to produce 1st liquid fraction containing sugars having carbon number of 5 and 1st solid fraction, heating 1st solid fraction in acidic medium containing acid at 2nd hydrolysis temperature for 2nd hydrolysis time to produce mixture, and hydrolyzing mixture with greater than or equal to 1 cellulase enzymes to produce 2nd liquid fraction containing sugars with carbon number of 6 and 2nd solid fraction. INDEPENDENT CLAIMS are included for:    (1) composition containing sugars having carbon number 5 or 6; and    (2) system for 2-stage production of sugars from biomass comprising slurry mixer containing 1st liquid at hydration temperature, rotary feeder that adds biomass to 1st liquid, dewatering chamber that removes liquid from biomass, cutter pump that reduces particle size of biomass and pumps biomass from slurry mixer to dewatering chamber, microreactor that reduces particle size of biomass to produce mixture of size-reduced solid particles, hemicellulose reactor where mixture of size-reduced solid particles is heated at 1st hydrolysis temperature and 1st hydrolysis pressure for 1st hydrolysis time to produce 1st liquid fraction containing sugars having carbon number of 5 and 1st solid fraction, 1st flash tank for reducing temperature and pressure of 1st liquid fraction and 1st solid fraction, 1st separator to separate 1st liquid fraction from 1st solid fraction, retention module mixer that mixes 1st solid fraction with acidic medium containing acid and heats 1st solid fraction at 2nd hydrolysis temperature for 2nd hydrolysis time to produce a mixture, and 1st enzyme reactor where mixture is hydrolyzed with greater than or equal to 1 cellulase enzymes to produce 2nd liquid fraction containing sugars having carbon number of 6 and 2nd solid fraction.