NOVELTY - The apparatus comprises: a housing (20H) having an inlet, an outlet and an axis (20A) extending through the housing, where the inlet is connected to a source of pressurized pretreated biomass while the outlet is connected in direct fluid communication with a downstream utility; and a stator (20S) and a rotor (20R) mounted within the housing. The stator and the rotor are confrontationally placed and spaced apart by an axial gap to define a mixing zone (20Z) communicating with the inlet and the outlet. The apparatus further comprises: a sensor operative to monitor pressure.    USE - The combined tangential shear homogenizing and flashing apparatus, is useful for destructuring pretreated biomass (claimed) including homogenizing cellulosic or lignocellulosic biomass such as aquatic or terrestrial plants.    ADVANTAGE - The apparatus provides inherently more stable performance due to the ability of the rotation to shear particles to a more acceptable size while systematically sweeping potential particle accumulations away from the flashing zone of the device, and efficiently destructuring the biomass with minimal time, investment and energy.    DETAILED DESCRIPTION - The apparatus comprises: a housing (20H) having an inlet, an outlet and an axis (20A) extending through the housing, where the inlet is connected to a source of pressurized pretreated biomass while the outlet is connected in direct fluid communication with a downstream utility; and a stator (20S) and a rotor (20R) mounted within the housing. The stator and the rotor are confrontationally placed and spaced apart by an axial gap to define a mixing zone (20Z) communicating with the inlet and the outlet. The apparatus further comprises: a sensor operative to monitor one of pressure, temperature, particle size and/or composition parameters of the pretreated influent biomass; an actuator for relatively displacing the rotor and the stator with respect to each other to vary the magnitude of the gap in accordance with the monitored parameter; an another actuator for varying a magnitude of a rotational speed of the rotor in accordance with the monitored parameter in responsive to the sensor; a flow diverter mounted between the rotor and the stator for conducting biomass into the mixing zone; and a cylindrical barrel mounted to the rotor. The barrel has a predetermined axial dimension, and extends axially from the rotor into nested relationship with the cylindrical portion of the rotor. The barrel and the cylindrical portion of the housing cooperate to define an axially extending milling zone between the barrel and the cylindrical portion. An axial dimension of the gap varying at positions radially outwardly from the axis with the axial dimension between the rotor and the stator is defined at a predetermined radial position, where the axial dimension between the rotor and stator defines a restriction to biomass flow. The restriction is placed adjacent to the radially outer edge of the mixing zone, and is placed not more than one-third of the radial distance inwardly from outer edge of the mixing zone towards the axis. The rotor is connected to a motor that rotates the rotor with respect to the stator such that rotational movement of the rotor with respect to the stator imparts a tangential shear to a predetermined volume of pretreated biomass introduced into the mixing zone at a predetermined pressure and temperature, in use, with a predetermined pressure difference defined between the inlet and the outlet, while the biomass is moving through the mixing zone in the direction of the pressure difference. The tangential shear homogenizes the biomass, and the pressure difference causes a partial phase separation of the homogenized biomass into vapor and liquid phases such that the pretreated biomass undergoes a three-fold total volumetric increase. The pretreated biomass undergoes a weight transition to a vapor of 1%. The axial dimension of the gap tapers uniformly from the axis to the radially outer edge of the mixing zone, and the smallest axial dimension of the gap defines the flow restriction. The stator has a cylindrical portion having a predetermined axial dimension. The barrel of the stator has an array of mixing enhancers. The barrel comprises an axially upstream end at which the flow diverter is mounted. The rotor and the stator are substantially disc-shaped members that are perpendicularly mounted to the axis of the apparatus. The monitored parameter is the pressure of the pretreated influent biomass.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic cross-sectional view of a combined tangential shear homogenizing and flashing apparatus.    Axis defined by housing (20A)    Housing (20H)    Rotor (20R)    Stator (20S)    Mixing zone. (20Z)