the hole nozzle plate 1 has a number of vertically and horizontally arrayed holes 1 a 1 from which jets of cold air are blown out to be impinged on to the back 3 a of the carcass 3 the slit nozzle plate 2 has a number of vertically extending parallel slits 2 a 1 from which jets of cold air are blown out to be impinged on eviscerated hollow 3 b of the carcass 3 in the surface freezing room cold air jets of u2212 20 u02dc u2212 45 u00b0 c are impinged on to the surface of carcass to freeze the subcutaneous tissue part to store latent cold heat there in the example of fig1 by spraying cold air jets of u2212 30 u00b0 c in the surface freezing room for 55 minutes the surface temperature of the carcass decreased to u2212 25 u00b0 c the surface freezing process will be explained in more detail with reference to fig2 a d fig2 a is a schematic sectional view of the tempering room with a carcass 3 transferred therein fig2 b is a schematic perspective view of the slit nozzle plate 2 and hole nozzle plate 1 fig2 c is a front elevation view partially cutaway of the slit nozzle plate 2 and fig2 d is a front elevation view partially cutaway of the hole nozzle plate 1 the slit nozzle plate 2 has a number of vertical slits 2 a 1 the slit nozzle plate.