It’s generally believed that riper cherries are more susceptible to pitting than less mature cherries, but Dr. Peter Toivonen, postharvest physiologist with Agriculture and Agri-Food Canada in British Columbia, said results of his research show it’s exactly the opposite. There are fewer pitting problems with darker cherries.
“For a lot of fruits, such as peaches and nectarines, we have always thought if you picked them a bit green, they’re harder and less susceptible to breaking down in shipment,” he said. “I think that’s where that logic came from with cherries.”
Growers often pick cherries before they turn mahogany, thinking they are less likely to break down before they get to market. Other times, they might decide to pick them red, rather than wait for them to fully ripen, in order to meet market demand at a particular time.
But research that Toivonen and his colleagues did at the Summerland research center, using Bing, Lapins, and Sweetheart cherries, showed that the fruit became less susceptible to pitting as it matured. Bing was the most susceptible of the three varieties overall.
Toivonen said there are three potential causes of pitting in cherries: physical damage, pebbling, and mildew on the fruit. It is well known that the temperature of the fruit affects the amount of pitting, with cooler fruit being more susceptible. Firmness also can be a factor.
For the experiments, Bing, Lapins, and Sweetheart cherries were harvested at a range of maturities—from light red to dark mahogany. Toivonen bruised the cherries using a design specially devised to induce pitting. The cherries were evaluated after two weeks in storage, and pitting was rated as superficial, medium, or severe. The experiment was done for two seasons.
Pitting was less severe in the more mature cherries in all three cultivars, even though the decline in firmness was different for each cultivar. Although previous research has shown that firmer cherries have more resistance to pitting, Toivonen’s work suggests that is not always the case.
Furthermore, he found no strong relationship between the amount of pitting and water loss from the cherry, nor did he see a relationship between pitting and the fruit respiration rate. He concluded that pitting could be related to several physiological factors, some of which might be more important in one cultivar than another.
Much of the damage that leads to pitting occurs during harvest, and there is no way to undo mistakes caused by the picker, Toivonen said. He believes that too little attention is paid to training pickers how to avoid damaging the fruit.
“Depending on the packing line you’re using, sometimes picking can cause 75 percent of the total problems, such as bruising and decay. It’s extremely important to work on that aspect.”
Though cherry season is always hectic, growers should make sure ahead of time that they have enough workers to pick the crop without rushing too much, he advised.
“If you want to pick without a lot of damage to the fruit, you’re going to have to have a lot of people to work with you, not just people who pick really fast, because it’s going to downgrade your quality,” he warned. “The fast picker is not something you really want. They bruise the fruit and loosen the fruit and in some cases, totally remove the stem.”
The more times the cherry is dropped and handled, the more bruises there will be. Workers should be trained not to drop cherries from a height into their buckets and be discouraged from handling the fruit.
After the cherries are harvested, placing reflective tarps over bins of cherries to protect them from the sun can make a big difference in maintaining quality.
Cherries should be cooled after packing, Toivonen said, because cherries often are not as cold as they should be when they go into the box. They should be held at around 0°C to 0.5°C (32 to 33°F), whereas they will often be at 2°C (36°F) or higher.
“Paying attention to the temperature of the fruit before you get it on the truck is very important,” he said. “Get it down as close to zero degrees (32°F) as possible.”
Toivonen made his remarks to an international group of fruit growers who visited the Summerland station this summer during a tour arranged by Susan Pheasant of Washington State and Mauricio Frias of Chile.