Research


Cherry softening project produces a sweet result


Sugarmeasurement at harvest found to be a key factor in setting quality standards.


By Judie Steeves T


here has been a breakthrough in research into the problem of softness in cherries. Peter Toivonen at the Pacific Agri-food Research Centre in Summerland


discovered that cherries with some compression injuries that cause softening in storage can actually heal themselves when held for one to 1.5 weeks in cold storage. He admits he’s excited at progress in his work on post- harvest impacts on cherries during picking and packing. “It’s been a stellar year in understanding why shippers experience certain situations,” he said. Usually it’s the fruit with lower sugars that go soft, while


those with high sugars are firm when picked and stay firm in cold storage, he noted. Discovery of the importance of the sugar measurement in


fruit at harvest allows quality standards to be set to ensure that only quality fruit is shipped. And, soluble sugars can be measured in the field by growers, using a hand-held refractometer. In fact, Toivonen says some growers have been using it to measure sugar levels in cherries at harvest for years. He believes the higher sugars create more turgor in the


cells, thus firmer cherries. With cherries, the sugar levels fluctuate, depending on such


factors as water stress prior to picking. Some softening, however, is probably not related to this


work. Impact bruising, such as when a cherry is dropped from a height, shows up as pitting rather than softness, he said.


Compression injuries are caused by squeezing too much


when picking, or when fruit is at the bottom of the pail and it’s weighted down. Toivonen plans to look more at where it occurs in the picking and packing processes this coming season. Up to now he’s looked at the Sweetheart variety, and will consider other varieties as well this year, but he has seen all varieties firm up in cold storage. Temperatures are critical with cherries, even if they’re only


being shipped short distances. If fruit is over 3 C in the box, no matter how long they’re


put in cold storage they will be soft. It’s important that forced-air cooling and a pyramid-style of packing cartons be used so all fruit is quickly cooled to the


14 JUDIE STEEVES


Peter Toivonen, right, of Summerland’s Pacific Agri- food Research Centre, with another well-known cherry researcher, Frank Kappel.


optimum temperature as soon as possible after packing. Forced-air cooling works much more quickly with pyramid stacking than when cartons are just stacked on pallets, and when the 10 kilogram cartons are just stacked, with spaces between the cartons, he found the temperature of the fruit actually rose instead of it cooling. So, palletizing doesn’t help lengthen the storage life of cherries. At 3 C and above, all fruit will go soft fast, but even firm


fruit won’t last more than three weeks, so chilling quickly after harvest is vital to maintaining high quality fruit. He encourages growers to keep the sugar levels of cherries


up by whatever techniques are possible, in order to prevent them from going soft. For instance, he said pruning to ensure good


photosynthesis is one important cultivation method to keep the sugars up, by removing the non-fruiting leaves. Toivonen said Aurora Golden Gala apples also appear to


heal compression injuries in cold storage. He’s working on some recommendations regarding that variety of apple in addition to his work with cherries.


British Columbia FRUIT GROWER • Spring 2012


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