Abstract: A batch process for the sterilization of particulate solid materials, in which a batch of particulate solid material to be sterilized is introduced into a rotary vessel shaped so that rotation of the vessel imparts a tumbling action to the solid material; the solid material is heated in the vessel while rotating the same to subject the material to a tumbling action; a lubricant liquid is injected under pressure into the vessel at a temperature in excess of the temperature of the solids; the lubricant liquid and solid material are held at a sterilization temperature while maintaining the tumbling action; and the sterilized solid material is withdrawn from the vessel under aseptic conditions.