TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The method (M1) involves 1) providing a mixture of biomass and an aqueous solution comprising ammonia where the dry weight of biomass is at least 15 wt.% relative to total weight of the biomass and aqueous ammonia mixture, and the aqueous ammonia is in an amount that is less than 12 wt.% relative to dry weight of biomass; 2) loading the biomass and aqueous ammonia mixture of 1) using a non-compacting feeder into an apparatus comprising a cylindrical barrel having a first end fitted with a piston and a second end fitted with a discharge valve, optionally an offset 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 in the cylindrical barrel or in the offset, a valve in the cylindrical barrel dividing the barrel into separate first and second chambers and first chamber having the barrel first end fitted with piston, and second chamber having the barrel second end with the discharge valve, and a flash tank attached to the discharge valve at the second end of the barrel, where the biomass is loaded into the first chamber of the cylindrical barrel or optionally into offset attached to cylindrical barrel; 3) closing off first chamber in the barrel and optional the offset; 4) optionally applying vacuum via least one port; 5) adding through the least one first port in the first chamber or optional offset, steam to reach a temperature inside the chamber that is 85-180 degrees C; 6) closing the ports in the first chamber and optional offset to provide an impermeable first chamber; 7) holding the biomass and aqueous ammonia mixture in the impermeable first chamber at suitable temperature for a time that is between 30 seconds to 4 hours; 8) optionally, moving the biomass and aqueous ammonia mixture through an opened valve into the second chamber of the cylindrical barrel by displacement with a piston through the impermeable first chamber where the biomass is not compacted; 9) optionally, closing the opened valve to form a second impermeable chamber and holding the biomass and aqueous ammonia mixture for a time that is between 2 minutes to 4 hours; and 10) moving the biomass and aqueous ammonia mixture by displacement with a piston following step 7) or step 8) through the discharge valve into the flash tank, where the biomass is not compacted. In the method (M1), at least one of step 1), 2), 3), 4), 5), 6), 7), and 8) are repeated at least once prior to 9). No de-compaction step is included. The aqueous ammonia is 4-6 wt.% relative to dry weight of biomass. The dry weight of biomass is at least 20 wt.% (preferably at least 30, especially at least 50) relative to the weight of the creating a biomass and aqueous ammonia mixture. The suitable temperature is 120-160 (preferably 140-150) degrees C. The non-compacting feeder of step 2) is a hopper (30) equipped with a non-compacting flow inducer. The first cylindrical chamber 32) is closed with at least one valve. The first chamber is closed with a first valve to close off the non-compacting feeder and a second valve (38) to close off the second chamber of step 8). The discharge valve is a gradual expansion venturi. The biomass is derived from multiple feedstocks. EXAMPLE - Whole corn cobs were processed with a jaw crusher (2.2 kW motor) with a jaw spacing of approximately 0.95 cm, followed by a delumper (RTM: ultra-sanitary crushers) (1.5 kW motor), followed by screening with a screen to fracture the whole cobs into smaller pieces. The small barrel piston reactor was charged with 115 g of fractured cobs, by hand placing of cobs into the end of the reactor with the piston removed. The piston was replaced to plug the end. A vacuum was applied to the reactor vessel to bring the reactor pressure to less than 10 kPa, and dilute ammonium hydroxide solution was injected to give an ammonia concentration of 4 g/100 g dry weight of biomass and a dry weight of biomass concentration of 50 g/100 g total biomass-aqueous ammonia mixture. After the ammonia solution was charged, steam was injected to bring the temperature to 145 degrees C inside the reactor. The biomass was held at temperature for 20 minutes and then discharged into the flash tank by activating the piston. During the 20 minute pretreatment, temperature was monitored and steam was added as necessary to maintain temperature. Pretreated cobs were harvested through the bottom of the flash tank. Excess free liquid was removed and remaining solids were used in saccharification. For saccharification, pretreated biomass (470) was added to the reactor. The pH of the contents was adjusted to approximately 5.5 by injecting citric acid buffer at pH 4.8 plus adding citric acid monohydrate. Once the desired pH was reached, Spezyme CP cellulase (RTM: cellulose) (25.8 mg/g) and hemicellulase enzyme consortium comprising beta -glucosidase, xylanase, beta -xylosidase and arabinofuranosidase were loaded into the reactor. Buffer, enzymes and water were added such that the final mixture in the reactor comprising pretreated biomass-saccharification enzyme consortium mixture (23 g dry biomass/100 g). The reactor remained in an incubator at 50 degrees C, rolling at 19 revolution per minutes for 72 hours to obtain total glucose release of 90%, total xylose release of 80%.