Rapid cooling of fruit
Apples need to be cooled as quickly as possible in order to provide the longest duration of storage and to provide the highest quality. This applies to fruit treated with chemicals post-harvest and to those left untreated. In this regard there are obvious benefits in not treating with chemicals as this only serves to delay prompt loading of stores.
To ensure that stores are loaded and the operating temperatures are achieved within 5 days of the start of loading the following points should be observed:
- The desired cooling rates will not be achieved unless the store is well insulated and there is sufficient refrigeration capacity to bring to bear during the pull-down period.
- Walls and ceilings should have 125 to 150 mm of expanded polystyrene or 100 to 150 mm of polyurethane.
- The construction of the floor should include 50 mm of heavy-duty polystyrene.
- The store air must be circulated quickly and distributed evenly through the whole of the stored product.
- The fans should be capable of producing forty changes of the store volume every hour.
- Allow at least a 50 mm gap between each tier of bins.
- Bins of fruit should be loaded into a store that has been cooled thoroughly for at least 2 weeks before loading.
- This ensures that the refrigeration plant is extracting primarily the field-heat of the apples and does not have to cope with undue heat ingress through the structure and to some extent the cold structure provides a small ‘ice-bank’ effect.
- It is important that during loading the refrigeration plant is switched off.
- The plant should be switched on when the door is not likely to be opened for some time.