There are three types of damage to cherries caused by vibration, impact and compression.
Types of damage (Continued from last issue)
Vibration
Vibration damage is the type of injury which results from cherries rolling around in bins while the cherries are being trucked to the packinghouse.
Warm cherries have greater susceptibility to roller or vibrational bruising than cold cherries.
Compression
Cherries on the bottom of the bin are subjected to compression forces while those on the top are bounced and rolled.
Since both compression and vibration forces damage warm cherries more than cold cherries, it is obvious that cooling cherries before transport will reduce damage.
This is especially important since an amount of fruit coming into the packinghouse is already bruised and damaged from compression forces.
Compression injuries cause bruising that ultimately leads to decay.
Compression bruising tends to be worse when the cherries are warm and can be caused by jostling fruit when it is transported from the orchard.
Cherries can also suffer compression damage at the packinghouse if they are stacked above the water level when they are emptied into the flumes.
Cherries with high soluble solid levels are less susceptible to compression injury because they also contain more water that increases the turgor pressure, making it harder to compress them than cherries with low soluble solid levels.
Hydrocooling cherries in bins at receiving areas quickly reduces temperatures and raises relative humidity within the bin. This is important in keeping good fruit quality.
Impact
Impact forces will damage warm cherries less severely than cold cherries. This is in direct contrast to compression forces which damage warm cherries more than cold cherries.
Studies in the USA have shown that cherries are more easily damaged at lower temperatures than at higher temperatures. Thus, to minimize pitting damage to cherries, the fruit should be run over the packingline as warm as possible.
This means, you must balance fruit quality against pitting damage.
We know that cold cherries are of higher quality since they respire and lose water at a slower rate than warm cherries. If pitting damage is a major problem, then you know that warm cherries suffer less pitting damage than cold cherries. If cherries are to be run over the packingline soon after receipt and pitting damage is a problem, then the cherries should probably not be cooled.
It is a trade-off between the inherent ability of the cherry to resist the impact forces applied during the packing process, the amount of impact forces the particular line applies to the cherries, and the length of postharvest life.
If cherries are held before being packed, cool them immediately. Hydrocooling or forced-air cooling will cool cherries 2.5 times faster than room cooling. However, studies in the USA showed that there was no difference in the cherries’ reaction to impact or compression forces when the cherries were room air or hydrocooled. Stem colour and shrivel were also unaffected.
Since hydro-cooling increases relative humidity and reduces the vapour pressure deficit, it should help keep cherries firm.
Sorting, packing and transporting cherries (cont next issue)
See this article in Tree Fruit March 2020
