A separator arrangement for a grinding machine that includes a grinding head, a rotatable advancement auger located within the grinding head, an orifice plate located within an opening defined by the grinding head, and a knife arrangement driven by the auger, comprising: a support arrangement adapted for interconnection with the grinding head and defining a support area positioned outwardly of the orifice plate; a separator chamber having a wall that defines an axially extending tapered separator passage, wherein the separator chamber defines an upstream end adapted for engagement with the orifice plate and a downstream end adapted for engagement with the support area of the support arrangement, wherein the separator passage is adapted to receive a mixture of soft material and hard material discharged by the orifice plate, wherein the wall of the separator chamber includes a plurality of perforations that communicate between the separator passage and an outer surface defined by the wall; and a separator screw disposed within the separator passage of the separator chamber, wherein the separator screw is adapted for interconnection with the rotatable advancement auger and is rotatable within the separator passage in response to rotation of the rotatable advancement auger, wherein rotation of the separator screw causes separation of soft material from the mixture of soft material and hard material and forces the soft material through the perforations in the wall of the separator chamber, wherein the downstream end of the separator chamber includes an outlet for discharging hard material from the separator passage; characterised by an adjustment arrangement for adjusting the axial position of the separator screw within the separator passage. a support arrangement adapted for interconnection with the grinding head and defining a support area positioned outwardly of the orifice plate; a separator chamber having a wall that defines an axially extending tapered separator passage, wherein the separator chamber defines an upstream end adapted for engagement with the orifice plate and a downstream end adapted for engagement with the support area of the support arrangement, wherein the separator passage is adapted to receive a mixture of soft material and hard material discharged by the orifice plate, wherein the wall of the separator chamber includes a plurality of perforations that communicate between the separator passage and an outer surface defined by the wall; and a separator screw disposed within the separator passage of the separator chamber, wherein the separator screw is adapted for interconnection with the rotatable advancement auger and is rotatable within the separator passage in response to rotation of the rotatable advancement auger, wherein rotation of the separator screw causes separation of soft material from the mixture of soft material and hard material and forces the soft material through the perforations in the wall of the separator chamber, wherein the downstream end of the separator chamber includes an outlet for discharging hard material from the separator passage; characterised by an adjustment arrangement for adjusting the axial position of the separator screw within the separator passage.