As production volumes increase for Honeycrisp apples, the need for a longer marketing window becomes more important. Researchers like Ines Hanrahan are looking for ways to stretch storage of Honeycrisp beyond Christmas.
With consumers and retailers clamoring for the popular variety, growers have responded to the strong demand by planting more acreage. But as volume has increased, marketers and shippers aren’t the only ones who want to extend the season. Retailers also want to sell the popular variety for as long as possible.
Hanrahan of the Washington Tree Fruit Research Commission has conducted preliminary research to see if Honeycrisp could be stored until February. She also wanted to learn how the cultivar performed under the different storage regimes of controlled atmosphere, dynamic controlled atmosphere, and regular air.
Honeycrisp is known for its chilling sensitivity and can’t be stored at temperatures as low as other varieties, she noted. Disorders like soft scald can show up within a week or so of harvest, and the variety is also susceptible to bitter pit and internal breakdown.
“But there’s a silver lining for the variety,” Hanrahan said. Honeycrisp loses very little firmness over time during storage and is much firmer than varieties such as Gala, she said.
She set up her trial to test fruit from uniformly cropped blocks with minimum alternate bearing from three different Washington State orchards (south—young orchard; north—mature orchard; and north central—organic orchard). Fruit were commercially picked at two different times, representing early and standard harvest dates, and segregated for storage. Cull fruit was eliminated before fruit were held from one to three weeks at 50°F and then put into the three storage regimes:
Regular air–37 degrees F.
Controlled atmosphere–37 degrees F, 0.5 percent carbon dioxide, 1.5 percent oxygen.
Dynamic controlled atmosphere–37 degrees F, 0.5 percent carbon dioxide, 0.7 percent oxygen. Under dynamic CA, the oxygen level changes according to the fruit response, which is why it’s called dynamic. The system monitors chlorophyll fluorescence to determine the ultra low oxygen level. “It’s like sending fruit into hibernation but without fermenting it,” Hanrahan explained. “When you reach the low oxygen limit, you then ramp up the oxygen to keep the fruit alive.”
Fruit samples taken at harvest were evaluated for quality, watercore, background color, bitter pit, and fruit minerals. Storage samples were analyzed monthly, from November to March, and, in addition to the attributes evaluated at harvest, were also monitored for soft scald, internal breakdown, off flavor, and greasiness.
Data shared by Hanrahan came from the 2008 harvest, stored through March 2009.
Preliminary results show little difference in firmness from both picks and from the three storage treatments. In the early pick, firmness differences showed up in February, but in the standard pick, firmness loss was only apparent in the regular air storage.
For bitter pit, the young orchard showed bitter pit at harvest. As expected, the incidence of bitter pit in the young orchard samples continued to increase over time, with higher levels of bitter pit found in the regular air treatment. Soft scald was not a problem in the lots sampled and didn’t show up in fruit samples until February.
The levels of soluble solids were relatively stable, ranging from 12.0 to 13.4° Brix at harvest. She found that the soluble solid levels were sometimes higher in the dynamic controlled and controlled atmosphere treatments than the regular air after prolonged storage.
Hanrahan found that all of the orchards and treatments had a big drop in titratable acidity after February. “This may be where we reached the end of the storage life for these apples.”
The sugar-acid ratios also changed significantly in March.
Honeycrisp stored in regular air showed significantly more greasiness than the apples from controlled and dynamic atmospheres. “The greasiness levels in the dynamic and controlled atmospheres never reached the same levels as the regular air,” she said, noting that peel greasiness developed in January.
In summary, though there is still much research to do, Hanrahan said that the fruit characteristics—sugars, acids, firmness, bitter pit, soft scald, internal breakdown, and off flavors—changed little during storage until March, indicating that storage past Christmas may be doable. She will continue to compare dynamic controlled atmosphere and controlled atmosphere to learn if there is benefit to using the dynamic system.