In the packhouse the crop is usually handled in one of two ways.
Problems with method 1: Leafy crops such as spring cabbage can warm up substantially during a protracted packing period. Also condensation can be a major problem. Warming-up can be reduced by allowing only a small amount of produce out of cool-store and onto the line at any one time, and by removing pallet loads of produce to the holding stores as fast as possible after packing. On occasions, this means moving half-filled pallets, rather than waiting for full loads to be produced. If considerable re-warming has occurred during the packing operation there are occasions when insufficient time remains to remove this heat after packing.
- Cool " pack " cool & hold
- Pack " cool " then hold
Method 2: When cooling after packing, the problem of re-warming does not arise as long as the product is moved to the holding store immediately after cooling. However, weight loss during cooling has to be allowed for in the weighing and packing operation.
Packing produce in the field: Field -packing, particularly of lettuce, is perfectly satisfactory provided the crop can be cooled immediately on arrival at the packhouse. In the case of lettuce this can be done quickly by vacuum cooling. However, not all crops can be vacuum cooled and where conventional coolers are used the design of containers affects the rate of cooling.
It is much easier to remove heat from produce in open sided plastic wooden crates or in trays with stacking corner posts, than in solid sided cardboard cartons. Although film packaging and overwrapping may reduce weight loss it also hampers cooling.
The Cool Chain
Many of the multiple stores operate the 'cool chain'. To be successful this requires close attention to detail and maintenance of cool temperatures right the way through to retail display. Several of the 'multiples' run depots at a temperature of 7°C. Produce below 2°C and above 10°C may be rejected. In the majority of cases packers attempt to cool produce down to around 3°C so that any re-warming that may occur during transfer to and from stores can be accommodated within the 7 - 10°C range. If dealing entirely with wholesale outlets it is generally preferable to cool from field temperatures to around 10°C rather than cool to 3°C and allow it to re-warm in the markets.