Maintaining cherry quality after harvest

Written by   Bas van den Ende and Ken Gaudion

The aim of this article is not only to develop an understanding of the importance of temperature management, but also to ensure that orchardists can grow a quality product that is big, dark, sweet and firm, and will have a reasonable shelf life.
High quality cherries also must have a low incidence of defects such as pebbling (rough pebbled texture of the skin), pitting, stem browning, shrivel, decay and softening.

People love to eat fresh cherries but few realise how difficult it is to keep cherries fresh.
The reason for this is that the cherry is a non-climacteric fruit. Non-climacteric means that what you harvest is what you get. Internal quality does not improve after harvest.
Cherries are also highly perishable because of their high respiration rate. When cherries are picked from the tree they are removed from their life support system and senescence begins. They also lose water easily during picking, packing, storage and transit because the cuticle (a waxy layer coating the outer wall of epidermal cells) is poorly developed.
Effects of temperature post harvest
Temperature management is a major challenge in maintaining good postharvest quality of cherries.
In the orchard, picked fruit must be kept in the shade and regularly collected and taken to the shed.
If cherries are in bins it is wise to use covers to maintain a cool transit to the shed.
Cherries at the shed can be cooled slightly by flushing copious amounts of water over the fruit and that will reduce fruit temperature by perhaps a couple of degrees Celcius.
Flushing the cherries with water will remove 98% of spores that can cause rots, be sure that the water is not flushed back into a re-use tank or hydro-cooler (B. Tompkins). Better still, put the fruit through a hydro-cooler and bring cherry core temperature right down under 5C.
Everything possible must be done by growers, transport companies and in packingsheds to quickly reduce flesh temperature throughout the postharvest life of the cherries.
All harvest and postharvest processes must be carried out with regard to their effect on fruit temperature to maximize shelf life.
These factors are extremely important when it comes to export of cherries. Fruit not cooled sufficiently may lead to poorer quality outcomes at the destination, and the possibility of lower returns.
The heat generated during respiration in cherries is significantly higher than in other fruit species, and is similarly affected by temperature.
As a general rule, every 10C rise in temperature just after harvest, reduces the shelf life of cherries by half. Conversely, lowering the temperature 10 degrees doubles the potential shelf life of cherries.
Since respiration uses the reserves of the food in the cherry, the rate of respiration is inversely proportional to the shelf life of the cherry (excluding decay problems). Cherry quality cannot be improved after harvest. You can only try to slow down the deterioration which begins the moment cherries are harvested.
To maintain quality, no phase in the postharvest handling procedure is more important than of initial cooling, or removing field heat from the cherries after harvest.
Cherries held at 21C lose more quality in one hour than they do in one week held at 0C. Decay increases and firmness and stem quality go down when cherries are subjected to high storage temperatures. Fruit respiration rates go up as the temperature climbs, resulting in shorter storage or shelf life.
Effects of temperature pre harvest
Cherries on trees expand in the cool of the night and shrink during the day. This is governed by both temperature and humidity in the orchard.
During the day, the cherries provide water to the leaves for transpiration. This is shown when, on a hot afternoon before harvest, the tree is not wilting. Yet the day after harvest, when there are no cherries to provide water to the leaves, the tree wilts. The only difference is that the fruit has been removed.
Irrigation is important to keep cherry trees supplied with water through the roots, but soil water alone is insufficient to prevent wilting on a hot day after harvest.
As ambient temperatures continue to climb during the day, the cherries need to supply the leaves with water. The hotter the day, the more water is needed for transpiration. When the ambient temperature is above 38C, the cherries weaken. Picking them results in soft fruit which cannot stand the normal rigours of postharvest handling.
A cherry is not an apple (cont next month)

See this article in Tree Fruit Sept 2019

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