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Cosmic Crisp (WA 38) starch scale. (Courtesy Washington Tree Fruit Research Commission)

Cosmic Crisp (WA 38) starch scale. (Courtesy Washington Tree Fruit Research Commission)

As the Washington apple industry gears up for the first commercial harvest of WA 38 this season, everyone wants to get it right. And ripe.

To that end, the Washington Tree Fruit Research Commission recently released the starch scale it developed to ensure optimum harvest timing for the apples, marketed as Cosmic Crisp. It’s an important tool — because of some of the unique attributes of the cultivar and the plans to ensure its successful launch.

“Four weeks before harvest, it’s nice and red, but we want to ensure that people are waiting until it is nice and ripe to pick,” said Ines Hanrahan, executive director of the research commission. “We’ll use it to determine at which point to pick it and at which point it is ready for sale.”

The scale for iodine dipped samples runs from 1 to 6, which is typical for Washington, but includes half points. That’s a response to industry feedback saying scales with more pictures work better, Hanrahan said. “There’s a better chance it hits exactly right,” she said.

The scale shows starch clearing from the core outward as fruit matures in two signature patterns, a flower pattern and a radial pattern. The finalized scales distributed to the industry this year are based on testing hundreds of apples from each of four orchards in both 2017 and 2018, before, during and after harvest, along with apples assessed after eight weeks in cold storage at 36 degrees.

That data shows that WA 38 ripens slowly, with little difference observed on fruit harvested almost a week apart, which provides for a long harvest window. It also ripens more uniformly than many other varieties, allowing it to be picked in one pass.

Using the starch scale may require more patience than many people are used to; it can take up to 5 minutes for the pattern to show, Hanrahan said, and cold temperatures make the process take much longer. For that reason, people may want to make the assessments in the afternoon, when fruit is warmer.

Preharvest field days will be scheduled to show people how the scales work, she added. •

—by Kate Prengaman

Online: Download this chart — or similar WA 38 starch scales — at treefruit.wsu.edu/wa38-starch-scale

Related: What Cosmic slices reveal