NOVELTY - Treating (M1) biomass involves loading the biomass using a non-compacting feeder into an apparatus containing a cylindrical barrel; adding an aqueous solution comprising ammonia (less than 12 wt.%) through a port (45) in the cylindrical barrel; creating biomass and aqueous ammonia mixture; closing the ports to make the chamber impermeable; holding the biomass/ammonia mixture in this chamber for 30 seconds to 4 hours; and moving the biomass and aqueous ammonia mixture with piston (34) through the impermeable cylindrical barrel through the discharge valve into the flash tank (42).    USE - For treating biomass (selected from switchgrass, waste paper, sludge from paper manufacture, corn grain, corn cobs, corn husks, corn fiber, corn stover, grasses, wheat, wheat straw, hay, barley, barley straw, rice straw, sugar cane bagasse, sorghum, soy, components obtained from milling of grains, trees, branches, roots, leaves, wood chips, sawdust, shrubs and bushes, vegetables, fruits, flowers and animal manure) useful in the preparation of the hydrolysate (claimed); and in the preparation of the fermentable sugar to produce valuable products such as fuels and other chemicals.    ADVANTAGE - The method involves treating biomass that moves high dry weight of biomass through a low-cost reactor while allowing for maximal accessibility by chemical reactants, to prepare the biomass for saccharification.    DETAILED DESCRIPTION - Treating (M1) biomass involves providing biomass; loading the biomass using a non-compacting feeder into an apparatus containing a cylindrical barrel having a first end (33) fitted with a piston (34) and a second end (41) fitted with a discharge valve (40), optionally an offset (31) attached at one offset end to the cylindrical barrel near the cylindrical barrel first end, and having a sealable valve at the unattached offset end, at least 2 sealable ports (45) in the cylindrical barrel or in the offset, optionally a valve (35) in the cylindrical barrel dividing the barrel into separate first chamber having the barrel first end fitted with piston and second chambers (39) having the barrel second end with the discharge valve and a flash tank (42) attached to the discharge valve at the second end of the barrel where the biomass is loaded into the cylindrical barrel or optionally into offset attached to cylindrical barrel; closing off the cylindrical barrel and optional offset; optionally applying vacuum via at least one port in the cylindrical barrel; adding through at least one port in the cylindrical barrel or offset an aqueous solution comprising ammonia (less than 12 wt.%), creating a biomass and aqueous ammonia mixture, and further the dry weight of biomass is at a high solids concentration of at least 15 wt.% to the weight of the biomass and aqueous ammonia mixture, and optionally adding steam through second port in the cylindrical barrel or offset to reach a temperature inside the barrel that is 85-180 degrees C; closing the ports in the cylindrical barrel and optional offset to provide an impermeable chamber; holding the biomass and aqueous ammonia mixture in the impermeable chamber at temperature for 30 seconds to 4 hours; optionally moving the biomass and aqueous ammonia mixture to a second chamber in the cylindrical barrel by displacement with piston where the biomass is not compacted, and holding it for 2 minutes to 4 hours; and moving the biomass and aqueous ammonia mixture with piston through the impermeable cylindrical barrel through the discharge valve into the flash tank. An INDEPENDENT CLAIM is included for the hydrolysate is produced by saccharification of the treated biomass produced by the method (M1).    DESCRIPTION OF DRAWING(S) - The figure shows a schematic drawing of an apparatus for use in the method.    Hopper (30)    Offset (31)    First cylindrical chamber (32)    First end (33)    Piston (34)    Valve (35)    Second valve (38)    Second chamber (39)    Discharge valve (40)    Second end (41)    Flash tank (42)    Port (45)    Tubing (46)    Condenser (47)