A method of reducing a temperature of at least one food product comprising: transporting the at least one item (32) within an enclosure (12) comprising at least one impingement apparatus (14)； providing: (a) a barrier (16) ,(b) at least one impinger (22), (c) a variable-speed gas circulation device (24) and intermittently performing an operation on the impingement apparatus (14) : (i) reducing a speed of the variable-speed gas circulation device (24) (ii) vibrating (40) the impinger (22) for breaking up snow and/or ice accumulated on the at least one impinger (22), and (iii) increasing the speed of the variable-speed gas circulation device (24) for returning the pressure differential to a pressure differential substantially similar to the pressure differential existing prior to said reducing the speed.
