Abstract: A grain polishing and whitening machine, particularly adapted for treatment of rice, comprises a base box, housing means having first, second, third and fourth coaxially arranged housing sections, said second housing section being coaxially mounted on said first housing section such that it may be rotatably displaced with respect thereto, said third section being coaxially mounted on said second section, and said fourth section being coaxially mounted on said third section such that it can be rotatably displaced with respect thereto, concentric hollow rotor means extending through said first, second and third housing sections, grain feed means in said second housing section, screw conveyor means within said second housing section and having a helical rib lined with an abrasive layer, for displacing and rubbing said grains along said second housing section and into the third housing section, cylindrical indented screen means in said third housing section adjustable, diametrically opposed, diagonally fluted kni