WSU Tree Fruit Research & Extension Center

Postharvest Information Network

Saturday, February 16, 2019

WSU-TFREC/Postharvest Information Network/Bing Cherry Maturity

Bing Cherry Maturity

Research at Prosser

Bing cherries are picked for shipping fresh while they are still ripening rapidly. Color becomes darker red, soluble solids increase, the fruit grows larger and it softens. Because the fruit are changing so rapidly, the time they are harvested is the most important orchard factor determining fruit quality. This report will show how color, soluble solids and size of Bing cherries change as the fruit progresses from briner to canning maturity and how the relationships among these characteristics are influenced by crop load.

The data to develop these relationships come from a nine-year study of Bing maturity conducted in the WSU orchard at Prosser (Figure 1). Samples were collected once a week, starting as color approached the USDA minimum and continuing until the fruit deteriorated from over-maturity. Several trees were sampled at each date. Three to five pounds of fruit per tree were picked from the ground. The pickers chose a limb then picked all the fruit on that limb to eliminate any bias toward selecting riper fruit. The sample was sorted into color categories designated "light red," "red" (BC color comparator No. 3 and USDA No. 1 minimum), "dark red," (BC color comparator No. 33) and mahogany. The fruit was weighed and counted to get the average weight per fruit. Soluble solids were determined on the juice of a subsample. Fairness was measured as the yield point of 120 g of pitted cherries.

Color Change

Color changed rapidly and at about the same rate each year. This probably is what led to general acceptance of color as the best maturity criterion of Bing. Figure 1 is an average of all the nine years showing the rate of color development in June and July. The rate was similar from year-to-year, but of course may have happened earlier or later than shown in the figure in any particular year. This figure may be useful to help estimate when picking will start. Samples collected at a packing house averaged 2.4 on this color scale.

Soluble Solids

Since color changes quite steadily and is our standard for maturity, we plotted soluble solids against color instead of date in Figure 2. Soluble solids increased during the harvest period but at different rates for different years. The "light crop" line is the average of the three lightest crops in the nine years, averaging 66 lbs. per tree. The three heaviest crops make up the "heavy crop" line, averaging 286 lbs. per tree. Soluble solids increased steadily as long as the fruit remained on the tree but much more slowly if the tree was heavily cropped.

Figure 2. Soluble solids and color of developing Bing cherries.
Comparison between three lightest and three heaviest crops in nine years.

These data illustrate that soluble solids are difficult to use as a maturity standard. It would be easy to set standards that could never be met with a heavy crop or that a light crop would meet before it developed color. Soluble solids would have merit as a quality standard but its adoption would require crop regulation by pruning or thinning to be sure the tree was not overcropped. It could also result in soft fruit being harvested as we waited for soluble solids to make the minimum.

Fruit Size

Large fruit are critically important in pricing Bing cherries (Figure 3). The leaf-fruit ratio, here represented by "light crop" versus "heavy crop" is the most important factor in determining size. Next most important is the harvest date. Fruit that was small because of over-cropping continued to grow until most of them were near mahogany color. In contrast the fruit on lightly cropped trees reached their maximum size near or shortly after fresh market maturity. Cherries could be left on heavily cropped trees to achieve greater size, as well as soluble solids, but this would increase the chance of the fruit becoming too soft to handle.

Figure 3. Fruit size and color of developing Bing cherries.
Comparison between three lightest and three heaviest crops in nine years.

Fruit Firmness

Fruit firmness data are not reported here. Our method for measuring firmness was unusual. No relationship with cropload was established but in all nine years the fruit softened progressively as they ripened. Some data have been published showing fruit becoming firmer as the cherries ripen beyond fresh market maturity. We have not observed this and believe it is safer, at present, to assume that the price of delayed harvest will be fruit that is more difficult to handle.

Use of This Data

These charts can be used as a basis for projecting changes in color, soluble solids and size of Bing cherries as they mature on the tree. They can be useful in making decisions concerning time of harvest and marketing strategies for a crop as it develops. The charts were developed from a limited data base. If the concept proves to be useful it would be possible to develop more comprehensive information. Please communicate your reactions to Dr. Gene Kupferman.

Ed Proebsting

WSU Irrigated Agriculture Research and Extension Center, Prosser

Post Harvest Pomology Newsletter, May 1983, Volume 1, No. 2.
May 1983

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