Conventional freezers for freezing large numbers of discrete items, such as food products, generally comprise a conveyor for carrying the discrete items into a freezing region, where the items remain for a predetermined period of time sufficient for them to be frozen to the desired degree, the frozen items then being conveyed out of the freezer. In such continuous freezing systems, the individual items are usually conveyed continuously into, through and out of an insulated container which is maintained at a low temperature, the individual items being frozen through contact with the low temperature atmosphere within the enclosure. In order to maintain the necessary dwell time, i.e. the time each item remains within the low temperature atmosphere, whilst maximizing the rate of product throughput and minimizing the space taken up by the system, such freezers generally comprise helical or spiral conveyors, such as that disclosed in U.S. Pat. No. 3,315,492.
A problem with such known mechanical freezers is that they are designed to freeze a maximum product throughput. Hence, they operate most efficiently at maximum throughput, but are inefficient at any other rate of throughput. Accordingly, such mechanical freezers are inflexible, since they cannot allow for changes in ambient temperature nor for variations in product throughput. Moreover, all such mechanical freezers become less efficient over time, with the consequence that the rate of maximum product throughput for optimal freezer performance gradually decreases. These disadvantages of prior art freezers are at least ameliorated and possibly eliminated in accordance with the present invention.