Abstract: A method and apparatus for mixing two substances under sanitary conditions in which a solid particulate substance is introduced into an inlet chamber with radial and downward velocity components and is mixed with a second substance in a mixing chamber below the inlet chamber by rotating a vertical shaft with mixing blades thereon in the mixing chamber. The mixing chamber is formed with a flexible wall which is deformed as the shaft rotates to prevent accumulation of mixed product on the wall. The vertical shaft is rotatably supported by bearings outside the inlet and mixing chambers so as not to contaminate the substances being mixed so that mixing takes place under sanitary conditions and the mixture of substances is discharged from below the mixing chamber. When the second substance is a liquid, the mixed product is an agglomeration of particles, a paste, a slurry or a solution.