Abstract: To practice the method of this invention, a large stainless steel tank having a conical bottom is utilized for the mass cooking of corn to produce masa. Connected to the conical bottom of the tank is a multiplicity of steam rings interconnected by a manifold to an external source of steam. A conical screen is positioned closely adjacent the conical bottom to facilitate the injection of steam for heating the contents and selective injection of air for stirring the corn in the cooking or steeping process. Interspersed closely adjacent to the steam rings are air injection rings receiving compressed air from the surge tank connected to a compressor. Selective injection of compressed air sequentially from the inner air ring followed by injection through the intermediate air ring and the outer air ring stirs the liquid and corn content of the tank in the process of cooking or steeping.