Abstract: A plurality of knives (100) carried by driven means (36) to travel in circular paths along an inside, cylindrical freezing surface (16) of a refrigerated double-walled drum (12) to remove salt water ice formed thereon. A substantially flat lower surface (122) extends along the bottom of a knife leading section (106) and a substantially flat lower surface (124) extends along the bottom of a knife trailing section (108). In a direction transversely to the length of knife (100), the leading and trailing lower surfaces (122, 124) are disposed substantially normal to the drum freezing surface (16), and in the direction extending rearwardly along the length of knife (100), the leading lower surface (122) is inclined slightly downwardly from the horizontal while the trailing lower surface (124) is inclined downwardly at an angle substantially greater than the angle of inclination of the lower leading surface (122).