OSU research ripens Comice, Bosc pears faster

May 29, 2008
David Sugar conducts experiments on pear trees at OSU's Southern Oregon Research and Extension Center. Photo: Tiffany Woods
David Sugar conducts experiments on pear trees at OSU's Southern Oregon Research and Extension Center. Photo: Tiffany Woods

CENTRAL POINT, Ore. – Consumers could be able to bite into fresh, sweet Comice and Bosc pears earlier than usual if pear handlers implement new ripening techniques tested by a researcher at Oregon State University.

Horticulturalist David Sugar has found that by briefly storing Comice pears at cool temperatures and applying ethylene gas to them, they could land in supermarkets by early September instead of the usual early October. With an even simpler version of that ripening treatment, Bosc pears could also be in shoppers' carts in early September instead of two weeks later, Sugar added.

"For consumers, under ideal conditions, this means that at their Labor Day picnics, they could be eating fruit salads made with flavorful Bosc and juicy, buttery Comice pears," said Sugar, who conducted the research in the orchard and lab at OSU's Southern Oregon Research and Extension Center in Central Point.

"For producers, this would extend their marketing season and hopefully allow them to bring in more revenue," he added.

Sugar said he focused on Comice and Bosc varieties because they make up the majority of the pears grown in southern Oregon's Rogue Valley. The valley is home to retailer Harry & David, which has built its business on selling gift baskets of mouthwatering, crème de la crème Comice pears marketed under the name Royal Riviera.

Pears, which are Oregon's state fruit, are finicky when it comes to ripening. They can get gritty when they ripen on the tree, so the custom has been to pick them when they're mature, then coax them into ripening through chilling and, in the case of Anjou pears, exposure to ethylene gas. With Comice pears, the traditional approach has been to pick them once they reach a specified firmness that tells the grower that the pears are mature. Then they're stored for at least 30 days at 31 degrees, and no ethylene gas is used.

Bosc pears, characterized by brown skin and firmer flesh, also are stored at 31 degrees, but only for roughly 15 days. They are not exposed to ethylene gas either. During this period both varieties develop the capacity to internally make ethylene gas, the hormone that fruits and vegetables produce to stimulate their own ripening. Pears don't produce it unless they're chilled after harvest or exposed to an external source of ethylene. Once they've developed the capacity to produce their own ethylene, Comice and Bosc pears need five to seven days at room temperature to fully ripen.

After two years of experiments, Sugar has developed new procedures to accelerate the ripening process with the help of ethylene gas. In his tests, he picked Comice pears after they reached the accepted firmness on the tree and put them in a room with ethylene gas for two days. Next, he stored them at 50 degrees and found that they needed only two days at that temperature to develop the capacity to ripen. They still needed the customary five to seven days at room temperature after that to actually ripen.

The bottom line: Comice pears don't need to be held in storage for a month before being shipped to grocery stores; only four days.

Sugar tested several other temperatures and periods of exposure to ethylene gas to create different ripening scenarios for Comice pears. None accelerated the ripening process as fast. For example, when the pears were exposed to one day of ethylene gas, then stored at 31 degrees, they needed 17 days at that temperature to develop the capacity to ripen.

Bosc pears behaved differently. He found that they didn't need to be placed in cold storage; they only needed to be exposed to ethylene gas for one day to develop the capacity to ripen.

In addition to studying how to get pears to market sooner, Sugar has been looking at how to keep Comice pears on the market longer. He tested a clear, plastic bag called LifeSpan that extends the storage life of pears by allowing them to absorb the oxygen and increase the carbon dioxide around them. Developed by an Australian company, the bags can add one to two weeks to the life of Comice pears while still maintaining high quality, Sugar said.

The bags are a low-cost option for packing houses, which line shipping boxes with them and then seal the bags. Traditionally, some packing houses have built airtight, controlled-atmosphere rooms and purchased machinery to generate a low-oxygen atmosphere to store pears. "But this bag has been widely adopted for a poor man's controlled atmosphere because you don't have to have an infrastructure, just a bag," Sugar said.

By using the bags and Sugar's new postharvest ripening method, Comice pears grown in the Northern Hemisphere could be on the market for up to six months instead of four to five months, he said. If packing houses in the Southern Hemisphere do the same, Comice pears would be available all year, he said, instead of being unavailable from February to early March and August to late September.

Author: Tiffany Woods
Source: David Sugar