Heat treatment of particulate solid material

In apparatus for preparing sterilized particulate solid material, comprising a sterilized vessel mounted on a pair of hollow trunnions for rotation about a generally horizontal axis and shaped so as to provide a tumbling action on particulate solid material therein as it rotates, a fluid inlet leading via one of said hollow trunnions, a source of cleaning and sterilizing fluids:

• the improvement that the vessel includes a discharge valve connected to the vessel at a point remote from the axis of rotation leading into a solids discharge duct passing out of the vessel via one of the hollow trunnions, and a supply line connected to said source and in fluid flow communication with the discharge valve, said supply line passing via one of said hollow trunnions for conveying cleaning and sterilizing fluids to the discharge duct, whereby the discharge duct may be cleaned and sterilized in preparation for discharge while the vessel is rotating.