Cherries that keep their cool travel better

How do you keep cherries fresh when exporting? The secret’s in the cooling, according to Canadian agrifood research.

Peter Toivonen, from Agriculture and Agri-Food Canada’s Pacific Agri-Food Research Centre, says that Canadian cherry producers have modified their logistics strategies to accommodate growing export markets. Producers have been challenged to find new ways of retaining fruit quality for weeks-long ocean crossings.

“All sweet cherry packing lines use hydrocooling to reduce fruit temperature before packing, which is compatible with the required speed and throughput of a typical packing line,” Toivonen explained. “Many packers in British Columbia have relied on either two- or single-stage hydrocooling to provide the sole cooling for sweet cherries.”

This technique is suitable for air freight, but less so for longer shipping via ocean container, Toivonen says. Cherries respire after packing, which generates heat. The packed heat can then accumulate significant heat over time in long-term transport or storage.

Toivonen analysed core temperatures of cherries after cooling and packing in the British Columbia cherry region. The study used temperatures from the low, middle and high end of industry standards to test the significance of temperature differences on cherry quality from hydrocooled packed boxes in a simulated long-term container shipping experiment.

He found that the core temperature of commercially hydrocooled fruit in palletised boxes was higher than the recommended temperature for cherries.

“Holding the cherries in a cold room, even when it was set at below 0°C, could not further lower the core temperatures of the sweet cherries in inner cartons of palletised boxes and, in another case, not even reduce the core temperature of sweet cherries in the exterior cartons of the pallet,” Toivonen said.

Toivonen’s analysis showed that the best consistently achievable core temperature for cherries is around 3°C, and that core temperatures could also be in the range of 5°C or more in some situations.

“A deviance of temperature as little as a few degrees Celsius can result in dramatically different outcomes for the most important quality indicators of sweet cherry,” Toivonen said. “Sweet cherries must be cooled after packing to bring their temperature down to a value that will ensure the best quality at distant markets when shipped by container.”

The best way to do this, Toivonen says, is forced-air cooling of palletised boxes.

The complete study and abstract are available on the American Society for Horticultural Science (ASHS) HortTechnology electronic journal website: http://horttech.ashspublications.org/content/24/4/457.abstract.