A method for sterilizing powder or grain, such that the method comprises: applying (11) heat and pressure, such that powder or grain (1) is supplied inside a heated gas flow conduit (104), maintained under heated and pressurized conditions, and the powder or grain is transferred while coming into direct contact with a vapor within the heated gas flow line (104), for between 0.008 and 2 seconds； sterilize (12) by instantaneous pressure reduction, such that steam and dust or grain are instantly released into a space that has a lower pressure than that of the heated gas flow conduit (104), of so that the water contained in the microorganisms that are attached to the dust or grain is boiled quickly, and the tissues of the microorganisms are destroyed； cooling (13) steam and dust or grain immediately after sterilization (12) by instantaneous pressure reduction, by means of air or a non-oxidizing gas supplied from a cooling unit (106)； and separating (14) the powder or grain, cooled, from the steam and from the air or non-oxidizing gas, such that in sterilization (12) by instantaneous reduction of the pressure, the steam and the powder or grain are passed to through a narrow tube or a hole provided downstream of the heated gas flow passage (104), in order to carry out a pressure reduction process, and the pressure reduction process is achieved between 0, 00001 and 0.1 seconds.Un método para esterilizar polvo o grano, de tal manera que el método comprende: aplicar (11) calor y presión, de tal manera que se suministra polvo o grano (1) al interior de un conducto (104) de flujo de gas calentado, mantenido bajo condiciones calentadas y presurizadas, y el polvo o grano es transferido a la vez que entra en contacto directo con un vapor dentro del conducto (104) de flujo de gas calentado, durante entre 0,008 y 2 segundos； esterilizar (12) por reducción instantánea de la presión, de tal manera que el vapor y el polvo o grano son instantáneamente liberados al seno de un espacio qu
