While harvested cherries are held in a loading area prior to transport, a hydrocooler will most likely be utilised to remove field heat.
Hydrocooling
Hydrocooling units typically consist of a large shower using chilled water to bring the fruit core temperature down as low as possible and practical.
Water used for these operations is recycled through a refrigeration unit and commonly treated with chlorine products to sterilise the fruit.
Due to the diverse geographical range that cherries are produced in, this loading area can be in a remote location and a portable hydrocooling unit can be set up on site, as witnessed in Washington State, USA (Figure 1).
These large units provide their own cooling and often their own power via a large portable generator, allowing hydrocooling to be undertaken in almost any environment.
Start of the cool chain
For most modern producers, hydrocooling represents the start of the cool chain.
From this point, harvested cherries will ideally remain in a completely controlled environment until the final point of retail sale.
Where fruit is grown in the same location as the packhouse, this hydrocooling is followed by fruit being transferred to a cool room where it will stay until being packed.
Although other utilised methods include forced air and passive room cooling, hydrocooling is the fastest and as such is commonplace throughout the world.
The chilled water moving across the fruit cools uniformly and under ideal conditions, cools about 15 times faster than passive air.
Despite shower-type hydrocoolers providing the most efficient cooling capacity, care must be taken to ensure operations are completed correctly.
Sanitiser
As the chilled water for hydrocooling units is generally recycled and treated with chlorine products, these levels of sanitiser must be properly monitored and maintained.
Often automatic dosing systems are used for this task although manual monitoring with test strips is still required.
Higher than desired levels of chlorine in treatment water can be detrimental to the fruit while lower levels could potentially expose equipment or water supplies to harmful bacteria.
Water drop height
Research has shown that decreasing the water drop height in shower-type hydrocoolers can significantly reduce the incidence of pitting damage in cherries.
Water drop heights of one metre could cause pitting damage to approximately 40% of all fruit directly impacted by water.
Conversely, water drop heights below 20cm reduced the amount of damaged cherries to under 10%. This figure lowers once again when a plastic mesh screen was added to diffuse the water and reduce water droplet size and velocity.
The same research showed that shower-type hydrocoolers were causing pitting damage to 18.6% of fruit and bruising damage to 9.6% of fruit in current systems at the time.
Pitting (cont next issue)
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See this article in Tree Fruit Sept 2021
