NOVELTY - The method comprises feeding a pretreated cellulosic biomass feedstock comprising precursors and reactants for bioreactions via a compression device to a centrifugal mixer comprising a rotor and a stator, rotating the rotor to disintegrate larger particle agglomerates of the pretreated cellulosic biomass feedstock, adjusting a temperature of the pretreated cellulosic biomass feedstock with gas, pressurizing the pretreated cellulosic biomass feedstock with gas, and pressurizing the centrifugal mixer to atmospheric conditions and a pressure of 0.2-1 bar.    USE - The method is useful for feeding biomass to a reactor for conversion into biofuel.    ADVANTAGE - The method is capable of precisely feeding the biomass to the reactor thus producing the biofuel with high yield and reduced entrainment of undesired organisms.    DETAILED DESCRIPTION - The method comprises feeding a pretreated cellulosic biomass feedstock comprising precursors and reactants for bioreactions via a compression device to a centrifugal mixer comprising a rotor and a stator, rotating the rotor to disintegrate larger particle agglomerates of the pretreated cellulosic biomass feedstock, adjusting a temperature of the pretreated cellulosic biomass feedstock with gas, pressurizing the pretreated cellulosic biomass feedstock with gas, and pressurizing the centrifugal mixer to atmospheric conditions and a pressure of 0.2-1 bar. The pretreated cellulosic biomass feedstock is further fed to a reactor via a second compression device and then subjected to enzymatic hydrolysis, a treatment microorganisms or fermentation. A liquid is added to the centrifugal mixer such that the liquid and the pretreated cellulosic biomass feedstock are mixed prior to feeding the pretreated cellulosic biomass feedstock to the reactor, where the liquid comprises water, enzymes, organisms or chemicals. A gas is added to the centrifugal mixer such that the gas and the pretreated cellulosic biomass feedstock are mixed prior to feeding the pretreated cellulosic biomass feedstock to the reactor. The precursors and reactants for bioreactions include sugars. The cellulosic biomass feedstock is pretreated with water, enzymes, organisms or chemicals. The rotor comprises: a full or partial disc having teeth for mixing that is mounted to a rotating disc; and vanes or blades to propel the pretreated the pretreated cellulosic biomass feedstock from a center of the centrifugal mixer to an outer edge of the centrifugal mixer. The stator comprises a full or partial disc having teeth for mixing that is mounted to a stationary disc. The teeth attached to the rotor are complementary with the teeth attached to the stator. The first and second compression devices comprise a screw press, plug feeder, or a sealed conveyor with a screw auger. The cellulosic biomass feedstock comprises agricultural residues, energy plants, or forest or sawmill residues.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of an apparatus for feeding biomass to a reactor.    Mixing system (100)    Motor (102)    Inlet (104)    Conduit (110)    Plunger (112)    Blow back valve. (114)