Tracking down pitting
Kotze started by determining when and where cherries were being damaged. He sampled fruit at every step from picking to packing. He also compared the occurrence of pitting in cherries transported in three different bin treatments. After sampling, the fruit was inspected for pitting within seven days.
The picked cherries were placed in rigid 15-litre totes. Pickers then either put the totes in standard wooden bins or emptied the totes into plastic maxi-bins. Kotze also compared maxi-bins with and without Fruitguard, a commercially available protective lining. Maxi-bins have the same footprint as conventional bins but are shallower.
Cherries must be cooled soon after harvest. They are typically transported from the orchard in three-bin trailers, as opposed to the seven-bin trailers used for apples. Despite their smaller capacity, the three-bin trailers are often not full when transporting cherries.
Unlike apples, cherries typically do not go directly from the orchard to an accumulation area and then by truck to the packhouse. Instead, the cherries are taken with smaller trucks to nearby depots for hydrocooling. Only then are they loaded on large, refrigerated trucks and taken to the packhouse.
Similar to the bin trailers, the smaller trucks are often partly empty, as their time-sensitive cargo doesn’t allow any waiting around for a full load.
While researching apple bruising, Kotze teamed up with consultant Henco Smit of Prima Defensio to monitor the impacts on fruit during handling. For the cherry project, Kotze employed a similar approach, placing loggers in various positions within bins and recording the size and number of potentially damaging impacts.
Pitting starts at picking
In his apple work, Kotze found that blaming pickers for bruising was mostly unjustified. But the same isn’t true for cherries. “The pickers play a large role in the initial damage,” he said. Therefore, it’s crucial to train pickers to handle cherries by the stem, not the fruit, and never to pull on the stems or drop the fruit.
Surprisingly, harvesting into totes that are placed directly in wooden bins did not result in less pitting than carefully emptying the totes into maxi-bins.
“The totes were considered a safe handling process, since there’s one less step where the fruit can be damaged,” said Kotze. He believes the disappointing performance of the totes is partly due to totes moving around in the wooden bins and partly due to the bigger combined surface area of all these small containers – 21 totes inside a bin.
Kotze’s apple trials showed that fruit in contact with surfaces is at a greater risk of damage than fruit in the centre of a bin, and that lining the bin helps protect the fruit. Although the same is true for cherries, they differ in an essential respect from apples.
For apples, bruising tends to increase from the surface to the bottom of the bin due to the upper fruit pressing down on the lower fruit. However, cherries are much lighter than apples, so fruit at the top of the bin bounces and rotates during transport, even with small vibrations, putting them at risk of pitting.
“Placing a wet sponge on top of the fruit in totes prevented them from moving, reducing damage,” said Kotze. “That’s something good we learnt.”
Kotze also sampled cherries at different points on the packline, concluding that current handling practices in the packhouse contributed negligible additional damage.
A bumpy ride
When analysing the data from the loggers, Kotze found that cherries are subjected to many minor impacts, mainly occurring during transport on the bin trailer and refrigerated transport from the depot to the packhouse, with far more frequent impacts during the latter.
Cherries are more susceptible to bruising once chilled, making the high number of impacts after hydrocooling especially concerning.
Kotze also tested the effect of partially empty trucks by comparing a 60% and a 30% load. He found that decreasing the load increased the number of impacts. This will happen with any vehicle, even a bin trailer, but it is less likely to occur in large trucks with air suspension than in small trucks with leaf-spring suspension.
Based on these results, he recommends adding weight when transporting partial loads. The cherries should be loaded first, as vibrations and impacts are more severe toward the back of bin trailers and trucks. The remaining space can be filled with anything heavy.
Dutoit Agri began adding load to partially filled trucks during the past cherry-harvesting season and saw a reduction in pitting. They also minimise impacts during transport by applying the lessons learnt from Kotze’s extensive trials on the prevention of bruising in apples.
Preventive measures include modifying bin trailers and forklifts, monitoring and adjusting the speed at which trucks and forklifts are driven, and maintaining surfaces on which forklifts are operated. Details are summarised in the best-practice guidelines for the prevention of bruising in apples, which are available on the Hortgro website.
