The “not so secret” success to ensuring that fruit and vegetables have a shelf-life far longer than the norm (particularly in cold storage) relies on three key factors, viz.
- consistent cold chain ambient temperatures that suit each different type of fruit & veg in storage
- constant high levels of humidity and
- continuous ethylene extraction
The idea is to replicate Nature to maintain fresh fruit and vegetables in prime condition in cold storage.
Cold room refrigeration chillers can control ambient temperatures with a fair degree of accuracy (provided cold room doors are not left unnecessarily open for extended periods). But chillers cannot control relative humidity and/or remove ethylene gas and additional interventions are therefore required to achieve those goals.
Fruit & vegetables require ethylene (among other ingredients) whilst in the soil to grow and flourish. Once harvested the DNA of the plant does not shut-down, it continues to produce ethylene, but now in a sealed-off air-tight chamber. The ethylene floats around, and for some plants post-harvest, it becomes a food spoilage gas in that it tends to ripen produce that is sensitive to ethylene. Qualitative loss of condition (less firm plant texture and eventual weight loss) which follows is the natural ‘costly’ consequence.
Simultaneously, fresh fruit & veg contain between 90% and 95% water during their growing phase which means that when conditions become too ‘dry’ inside a cold room, the post-harvest produce in cold storage will shed moisture; lose qualitative condition and texture; and finally lose weight.
Not necessarily in order of importance, but absolutely imperative (even for a few hours), is that the relative humidity (RH) remains constant at between 90% to 95% and that as much as possible of the ethylene gas is extracted from the sealed chamber.
An industrial humidifier coupled to a humidistat and humidity probe will maintain RH at any desired % provided a decent system is installed.
The more challenging factor to control is that of ethylene extraction which is usually undertaken via an ethylene scrubber. The problem with this type of mechanical removal methodology is that ethylene scrubbers are typically stand-alone units which have to be placed ‘somewhere’ in a cold room in the hope that it will extract sufficient volumes of the food spoilage gas to be effective.
The more savvy approach would be to place an ethylene scrubber at the rear of the evaporator cooler before the air is re-circulated back into the cold room. The only ‘scrubber’ that could be installed at that height behind an evaporator cooler and work effectively would be an ultraviolet unit with special UV lamps that oxidise ethylene gas. Such an installation will simultaneously keep the rear filters of the evaporator unit in a sterile and hygienic condition.
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