Abstract: An endless steel band or belt (12) moves upwardly (see arrow 65). The upper length or run (17) of the band or belt (12) is cooled or heated by a fluid flowing from nozzles (43, 59). A feeding station (21) supplies a liquid mixture which mixture runs downwardly along the crystallizing surface (11) of the belt. A crystal layer is thus formed on the crystallizing surface 11. This crystal layer is moved upwardly in counter-current. The remaining liquid, the mother liquor, which is substantially free from crystallizable substance, flows downwardly. A device (22) for changing the inclination angle (.alpha.) of the crystallizing surface permits the crystallizing device to be adjusted in a simple way in accordance with the requirement of the crystallizating process. For automatic operation, a control unit (C) can associate the angle of inclination (.alpha.