The linear relationship between temperature and cherry respiration rate, and the associated link between respiration rate and rate of fruit deterioration, indicates that the longest possible shelf life is achieved when fruit is stored at as low a temperature as possible.
Post packing cooling (cont from last issue)
The relationship between sugar content and freezing temperature has shown that fruit with high sugar content (22.5% brix) freezes at minus 2.5C, while fruit with low sugar content (16.7% brix) freezes at around minus 1.8C.
With these factors in mind, it is recommended that sweet cherries be stored between –0.5C and 0.5C.
Packing procedure
• Most Australian cherry packing follows a similar procedure:
• Full bins or totes of fruit are received from the field.
• Bins are hydrocooled to remove field heat.
• Bins are stored in cool rooms at 0C to 1C for one to three days.
• Fruit is graded with chilled water flumes to transport fruit to sorting tables within an insulated packing room.
• Fruit is packed into sealed boxes, random weight bags, or punnets and palletised.
• Palletised fruit is held in cool rooms between 0C and 1C prior to dispatch.
Fruit handled in this manner is highly unlikely to have a pulp temperature lower than 3C to 5C at time of palletisation.
Using these systems, cherries can only effectively be cooled through initial hydrocooling and passive room cooling during pre-packing storage.
Chilling of fruit with transfer flumes will most likely maintain current fruit pulp temperature without significant further chilling.
Several cherry packing lines have in-line hydrocooling systems installed which allow fruit to experience most of the earlier, rougher packing procedures at a warmer temperature (6C to 10C) before entering a submerged or shower-type hydrocooler immediately before de-watering and box filling.
Packing fruit under these conditions offers several advantages, the main one being the increase of fruit pulp temperature during the earlier packing processes will result in less fruit sustaining pitting and bruising damage.
However, most in-line hydrocooling systems will fail to have the cooling capacity to remove this excess heat and thus final pulp temperatures at box filling will still be in the range of 2C to 5C.
(cont next issue)
See this article in Tree Fruit February 2022
