The invention concerns a device comprising a rotary shaft (2) supported above a layer (C) of material, transversely to the translation direction (A) of the material, and means for turning (3) the material extending at least partly radially relative to the shaft (2) and rotated by said shaft to penetrate into the layer. The device comprises means for cutting (4) the layer (C) of material, radially spaced apart (g) from the rotary shaft (2) and rotated by said shaft, said cutting means (4) being located substantially on a cylindrical surface sharing a common geometrical axis with the rotary shaft, and capable, upon penetration into the layer, of fragmenting the latter, while the turning means causes the fragmented material to be granulated.