Pre-cooling
Pre-cooling is the term used to describe the extraction of field heat from the crops prior to storage. The advantages of pre-cooling are the rapid cooling of produce to storage temperature and a reduced demand on the main store cooling capacity.
- Forced air-cooling uses the principle that the rate of heat transfer from product to air increases with increasing air speed.
- With this technique a high-speed current of cold air is directed on to the product.
- It is possible to adapt most apple stores for use as forced air coolers using a plenum or tarpaulin sheet.
- The practice of leaving fruit out over night to cool should be avoided.
- On cold nights in September the air is usually still thus there is no air movement around the fruit and thus very little cooling effect.
- The cold night air does increase the efficiency of the condenser and thereby increases the rate that heat can be transferred from the product to the outside air
Duration of storage and storage conditions
Generally, the longer that fruit are held in store the more susceptible they become to rotting by fungi and to superficial scald and calcium-dependent disorders such as bitter pit. It is particularly important to avoid storing fruit to the point where their resistance to rotting is lowered.
- It is important to market fruit within the periods suggested for any particular storage condition and to monitor fruit regularly in order to gain advance warning of significant rot development or deterioration in fruit quality.
- CA conditions will not prevent infection of fruit in store although the composition of the atmosphere can influence the degree of rotting in store.
- In Cox, CA conditions that are low in oxygen and high in carbon dioxide are more conducive to rotting than low oxygen only. Growers should ensure that Cox apples for medium or long-term storage are kept in low oxygen/low carbon dioxide conditions particularly where there is a history of rot problems.
- Fruit harvested from Bramley orchards seriously affected by Nectria canker should not be stored in 5% CO2 + 1% O2 (5/1) due to an aggravated development of Nectria fruit rots.
Ensure that the most appropriate conditions are used for the period of storage that is anticipated. Termination dates that are recommended should be a guide only since the quality of consignments in store is likely to vary from orchard to orchard and from season to season.
Optimal quality can only be achieved by ensuring that consignments have adequate storage potential with respect to mineral composition and maturity at harvest.
Careful monitoring of fruit condition throughout the storage period is required to ensure that quality retention is in line with expectations. Those responsible for the storage of fruit should be fully aware of the notes that are included in the recommendations issued by East Malling Research (EMR) since these may be vital in achieving a successful outcome.
Information provided in this Section should be consistent with that provided in the wall chart (‘UK Storage Recommendations for Tree Fruit’) which was revised and published by AHDB in 2016 and mailed to all UK tree fruit levy payers.
It is difficult to set precise termination dates for the storage of any variety, as there are so many variables involved. Provided the fruit has adequate storage potential, the termination dates that are advised should result in quality product. It is essential that:
Stores are loaded in 2-3 days and the operating temperatures are achieved within 5 days of the start of loading.
The delay between picking and the start of cooling does not exceed 24 hours.
Final CA conditions are achieved within 14 days of the start of loading unless indicated otherwise.
Independent checks of store CO2 and O2 levels should be made regularly using portable analysers and drawing atmosphere sample direct from the store.