|Notes on a short talk about the different grape cooling systems given by our MD Mr Gerhard Potgieter last year|
Because respiration rate increases exponentially with temperature of the grapes, it is very advantageous to lower the temperature to below 20°C as soon as possible after picking and to below 10°C as soon as possible thereafter. At picking temperature of 30°C grapes respire 8 times faster than at 10°C and at packing temperature of 20°C 4 times faster than at 10°C.
How one achieves this reduction in temperature is very dependent on the overall system which is being followed from packing to market.
A producer with own cooling facility and containerising his product on the farm is able to use systems which would fail if attempted by a producer delivering to a central cold store which in turn dispatches to a secondary cold store for storage and thereafter via conventional ships to overseas ports where a plethora of handling and storage facilities is available.
There is no "ONE SIZE FITS ALL" refrigeration system which is ideal for all applications. Take cognisance of the entire handling and storage logistical chain and plan the associated refrigeration system requirements accordingly.
Changes are taking place in packaging design and marketing (new marketers, new market countries, new systems, etc). Under these circumstances one must try to build as much flexibility into new facilities as you can so that changed conditions can be accommodated later.
Attempt to do a cost vs benefit analysis before spending a disproportionate amount of capital on refrigeration systems. Ensure that spending is in proportion to benefit and to the expenditure on the other aspects of your table grape production. Refrigeration cannot improve the inherent condition of poor quality products.
Some features of the main refrigeration systems follows:
COOLING SYSTEMS FOR PRIOR TO PACKING
- combining with evaporative cooling
- fog spray
- wet coil
Typical operating cost for larger installations is 25 – 50c/carton.
POST PACKING COOLING SYSTEMS
– low desiccation of naked fruit
– no advantage for unperforated bag packaging
– no plastic bag in carton
– shrink-wrap complete pallet once cold
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