A mixer comprising: a vessel defining a mixing chamber therein surrounded by boundary walls for receiving a mixture containing lumps therein; a plurality of mixing blades ; and a driving mechanism supporting the mixing blades in the mixing chamber for mixing motion relative to the vessel so as to mix the mixture within the mixing chamber of the vessel ; the mixing blades including at least one lump conditioning blade having a rigid body terminating at a working edge along an outer side of the rigid body; and the driving mechanism supporting said at least one lump conditioning blade such that the lump conditioning blade is movable in a working direction along a respective one of the boundary walls; the working edge of said at least one lump conditioning blade being supported at a prescribed space from the boundary wall which is to reduce a lump size of the lumps in the mixture as the mixture passes between the working edge of the lump conditioning blade and the boundary wall; at least one primary blade having a rigid blade body terminating at a working edge along an outer side of the rigid body and which is supported by the driving mechanism so as to be movable in a working direction along a respective one of the boundary walls; wherein the working edge of said at least one primary blade is supported by the driving mechanism directly adjacent the boundary wall so as to (i) be in closer proximity to said one of the boundary walls than the working edge of said at least one lump conditioning blade and (ii) be arranged to scrape the mixture from said one of the boundary walls, characterized in that the working edge of said at least one lump conditioning blade is oriented substantially parallel to the respective boundary wall and at an angle relative to the working direction between 60 and 90 degrees. a vessel defining a mixing chamber therein surrounded by boundary walls for receiving a mixture containing lumps therein; a plurality of mixing blades ; and a driving mechanism supporting the mixing blades in the mixing chamber for mixing motion relative to the vessel so as to mix the mixture within the mixing chamber of the vessel ; the mixing blades including at least one lump conditioning blade having a rigid body terminating at a working edge along an outer side of the rigid body; and the driving mechanism supporting said at least one lump conditioning blade such that the lump conditioning blade is movable in a working direction along a respective one of the boundary walls; the working edge of said at least one lump conditioning blade being supported at a prescribed space from the boundary wall which is to reduce a lump size of the lumps in the mixture as the mixture passes between the working edge of the lump conditioning blade and the boundary wall; at least one primary blade having a rigid blade body terminating at a working edge along an outer side of the rigid body and which is supported by the driving mechanism so as to be movable in a working direction along a respective one of the boundary walls; wherein the working edge of said at least one primary blade is supported by the driving mechanism directly adjacent the boundary wall so as to (i) be in closer proximity to said one of the boundary walls than the working edge of said at least one lump conditioning blade and (ii) be arranged to scrape the mixture from said one of the boundary walls, (i) be in closer proximity to said one of the boundary walls than the working edge of said at least one lump conditioning blade and (ii) be arranged to scrape the mixture from said one of the boundary walls, <EOS>