Tree Fruit 2022

Improving sweet cherry fruit quality—cooling & packaging (part 11)

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.

Forced air cooling (FA)
FA cooling, also known as pressure cooling, is a post-packing process in which chilled air in a cool room is sucked through vent holes in the sides of palletised boxes. (continued from last issue)
All FA cooling systems are most effective when operating in a dedicated cool room, separated from the temperature fluctuations of doors opening and closing and new batches of warmer produce arriving.
This style of cooling and operating set-up was viewed at numerous sites across Chile and the United States and clearly appears to be the preferred method to cool cherries after packing.
Portable tunnel cooling units can be utilised in existing cool rooms although this often requires an upgrade of refrigeration to handle the increased heat load.
Currently, all cherry producers in Chile use FA cooling to lower cherry pulp temperature as much as possible before dispatch. For these pack houses, this is a minimum requirement for fruit to withstand the 20+ day sea journey to be marketed in China.
Achieving such a low pulp temperature requires palletised cherries to be cooled in purpose-built FA rooms for 10–24 hours with -0.5C chilled air.
Shipping fruit any warmer than this from Chile would not enable it to survive the journey to Asia in acceptable, marketable condition.
Increased shelf life
Renown cherry researcher, Prof. Juan Pablo Zoffoli, is a vehement believer that packing fruit at a warmer initial temperature and removing heat after box filling has been the key to increasing shelf life of cherries grown in Chile.
Speaking to cherry growers around the globe, Prof. Zoffoli has not only continued to stress the importance of this shift in mindset but has himself undertaken research to justify this considerably different concept.
When asked to comment on current packing systems used in Tasmania, Prof. Zoffoli was adamant that “packing cherries at such a cool temperature was most likely causing considerable damage” with his research indicating that fruit packed at 6C suffers less than half the pitting of fruit packed at 3C.
With considerable government and industry body funding which has fuelled cherry handling research in the country, many believe that a cherry shelf life of 60 days can soon be achieved. Although this time frame would be considered overkill for Tasmanian producers, the successes of the Chilean industry largely prove that these cherry handling techniques and procedures lead to the greatest extension of shelf life currently seen in the world.
(cont next issue)

See this article in Tree Fruit May 2022

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