Abstract: Method and apparatus for producing pulp from moisture-containing lignocellulosic material, such as wood chips, which is ground in a grinding space defined between a pair of grinding discs which rotate relative to one another in an environment of pressurized steam generated during the grinding process, in a closed housing. The ground fiber or pulp discharged from the grinding housing is propelled by the accompanying steam into a cyclone, where the ground pulp is separated from the steam for further treatment, while the steam is recycled for further use in the pulping process. The pressure in the cyclone is so controlled that a pressure is maintained therein which is substantially equal to a pressure drop which is sufficient merely to maintain the propellant force of the steam to convey the ground pulp from the grinding housing to the cyclone while discharging the separated steam and recycling it for further use in the pulping process.