In a method for implementing mechanical, chemical and/or thermal processes in a product which is located in a housing (1) with mixing and cleaning elements and/or transporting elements (6) on at least one shaft (4, 5), and is transported via said elements (6) from an inlet (2) to an output (10), the intention is for a cross section of the housing (1) to be adjusted in variable fashion at least once in the longitudinal direction thereof.