The invention relates to a method of treating substances in divided solid form for thermal debacterization, in which the substances are stirred in a closed enclosure provided internally with controlled heating contact wall means acting directly on the substances while they are being stirred. In accordance with the invention, the substances for treatment are previously mixed, prior to reaching an inlet to the closed enclosure, with an anti-clumping agent likewise in the form of divided solids, the mixture then being stirred in the closed enclosure while being subjected to the combined action of the heating contact walls and of the superheated wet steam, and being recovered at an outlet of the closed enclosure.
