A surface-worked granular product is produced by supplying raw granular material to a cylindrical retainer having apertures and retaining sites, floating the granular material by suctioning air from the cylindrical retainer, rotating a rotary working device installed in the cylindrical retainer, and contacting working protrusion protruding from the working device with the granular material to remove foreign substances and to perform surface-working of the granular material so as to form a rough surface without causing degeneration, denaturation or substantial removal of useful ingredients, wherein the surface-worked granular product has surface characteristics different from raw granular material.

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