The challenge is getting the cherry to separate at the upper abscission zone at the twig.
In the complex world of sweet cherries, one market is calling for light-colored sweet cherries with stems on for processing, and is willing to pay three to four times the normal processing price to get them.
The demand for stem-on cherries is coming from Gray & Company, the world’s largest producer of maraschino cherries and glacé fruit. Headquartered in Portland, Oregon, it has two manufacturing plants, one in Oregon and one in Michigan.
Cherries for processing can be harvested mechanically and handled a lot less tenderly than cherries for fresh market, so it’s a less costly process. Moreover, there’s profit to be made from high yields of smaller cherries, because maraschinos are usually 12-row and smaller.
A key problem, however, is that when cherries are shaken from trees, they want to leave their stems behind. And while stemless cherries can also be processed, they have not enjoyed good prices lately. They’re only worth about 18 cents a pound.
Jeff Send, a cherry grower from Suttons Bay, Michigan, sold 1.25 million pounds of sweet cherries to Gray & Company last year and also runs a receiving station for the company. Last winter, he had 20 brine pits holding 3 million pounds on his farm. He’s a leader in the “go for stems” movement.
“Do the math,” he said. “There’s a lot of difference between 18 cents and 50.”
Over the last few years, as the market for stemless cherries softened, Send and several of his neighbors began to look for ways to get more sweet cherries with stems. At Gray & Company, chief executive officer Jim Reynolds had been putting out signals that the company would pay growers more for them.
Moreover, Reynolds said, the company invested $1.6 million in its plant in Hart, Michigan, so they could separate cherries both by size and by whether they have stems or not. Growers would be paid according to packout. For growers, the challenge is getting cherries off the trees with stems but without having the cost of picking them by hand.
Last summer, Michigan State University horticulturists Jim Flore, Nikki Rothwell, and Greg Lang put together a research team to see if they could help growers out. They mechanically harvested three varieties of sweet cherries every day from July 2 to July 17. They worked in growers’ orchards, including Send’s, at three Michigan locations. Julia Rice, a recent graduate of MSU, ran the harvester and collected the data.
Several measurements were taken—fruit size, stem length, fruit removal force, soluble solids, and growing degree-days. Some trees were hand-thinned to see whether cherries borne singly on a spur harvested differently from those in clusters. The effect of ethephon (Ethrel), the plant growth regulator that has been used for 40 years to loosen sweet cherries for machine harvest, was studied as well. Cherries were tested after brining to determine whether stems stayed on or came off later.
The results, Flore said, showed that when fruit removal force fell under 300 grams, cherries came off at the lower abscission zone near the fruit and so were stemless. Less-mature fruit would come off at the higher zone near the branch, with stems on.
Side to side
To remove cherries, the shaking action has to be side to side, not up and down, Flore said. Cherries being shaken move like a pendulum, and heavier fruit and longer, stiffer petioles were more likely to detach at the twig. Stiffer petioles came off easier than thinner ones. Five-gram cherries on 1.5- to 2.0-inch petioles came off best.
Early harvest when fruit was just starting to turn color resulted in a higher percentage of stems, but the high fruit removal force resulted in trash in the totes as leaves and twigs came off, too.
Send had discovered much the same. “The key to mechanically harvesting is to keep the machine moving and don’t look back,” he said. “You may think you’re leaving too many cherries on the tree, but shaking more damages the tree, doesn’t take off much more fruit, and gives you lots of trash.”
Gold, a variety that has highly desirable, smaller fruit, did not harvest well with stems on, Flore said. While processors like the light-colored cherries like Gold and growers plant it as a processing variety, it is not a good candidate for stem-on harvest because of its willowy wood, he said.
Rothwell, coordinator at the Northwest Michigan Horticultural Research Station, hand-thinned several trees to eliminate clusters, but the data showed thinning had little or no effect. Single cherries didn’t harvest better or worse than clusters.
The grower practice of using ethephon to loosen cherries to make harvest easier with less trauma to trees really works—but at the lower abscission zone. Virtually no cherries treated with ethephon came off with stems on. Moreover, Reynolds said, stems still on at harvest fell off later during the curing process.
“There is no chemical we know of that you can use preharvest that will help make cherries come off with stems,” Flore said. “Definitely do not use ethephon if you want stems.”
Cherries with stems kept them throughout the brining process, the researchers found, unless they were treated with ethephon.
The other two varieties in the test were Emperor Francis and a dark variety, Ulster.
Flore said additional research would be done to refine the process as they study optimal shaker oscillation and length of shaking bursts. A newer processing variety, Andersen, released two years ago jointly by MSU and Cornell (and named after retired Cornell cherry breeder Bob Andersen), will also be tested.
For now, Flore said, the practical advice for growers is: “Try to harvest early. Do a test to see how many leaves are removed and hold off a day or so if necessary and try again.”
Send said growers really need to know their orchards. “The harvest window is quite narrow,” he said. “You have to be there when the cherries are ready.”
In addition, tree pruning is important, since trees with willowy, pendent wood did not shake as well as trees with shorter, stiffer limbs.
Send worked with Gray & Company to develop a program for growers. A grower has to commit at least 50 plastic totes of cherries, each holding about 750 pounds. Last year, growers around Grand Traverse Bay harvested 3,000 totes.