Abstract: A culture medium preparator includes a cylindrical vessel that terminates at the low part in a substantially hemispherical cap, a lid and a stirrer placed in the vessel. The stirrer includes a vertical tube placed in the center of the vessel, a plurality of blades put into rotation about the tube and magnetic masses at the periphery so that they are placed in proximity to the internal wall of the vessel. The preparator furthermore includes a magnetic ring in rotation about the internal wall at the same height as the magnetic masses. The magnets attract the magnetic masses, the magnetic ring being moved in rotation by a motor. In this way, the stirrer is driven in rotation without requiring mechanical elements placed inside the vessel, the absence of such elements facilitating the cleaning.