Apr 7, 2007

Scramble Toward Sweet Cherries Is On

Why do sweet cherries crack?

The easy answer is, “It has something to do with rain.”

But, conceded Mortiz Knoche, he didn’t have to come all the way from eastern Germany to tell growers that.

He was the leadoff speaker in a four-day cherry symposium in Traverse City, Mich., in January that drew experts from all over the world. The first two days were devoted to growers, then the scientists stayed two more days to share cherry information among themselves.

Knoche, from Martin Luther University in Halle, Germany, did offer some real insight about why sweet cherries crack. The reason is, simply, sweet cherries produce a fixed quantity of skin and spread it over an expanding mass of fruit flesh. The skin gets thinner and thinner.

So, in one sense, rain isn’t the culprit. Under a microscope, sweet cherries show tiny cracks, perpendicular to the elongation of cells, long before they are fully mature. Rain, hydrocooling, even high humidity can deal the final blows that produce the big crack.

The tiny cracks already represent a disruption of the barrier the skin is supposed to provide against disease organisms.

“It explains why fruit sometimes rots so quickly after harvest,” Knoche said.

The ideal solution to cherry cracking would be more, looser skin, but Knoche provided no insight on how that might be possible. Since rain itself can’t be blamed, even measures that protect cherries from rainfall won’t be entirely effective. Cherries crack because they’re cherries and it happens all over the world.

Other speakers examined protective measures, and the use of protective covers is becoming a worldwide practice, according to John Cline from the University of Guelph in Ontario, Canada.

The problem of cherry quality, coupled with good prices and demand for cherries over a longer season, is changing the way growers grow cherries. Protective covers, usually high tunnels, provide frost protection, allow cherries to stay on the trees longer and become larger and sweeter, provide protection from birds and reduce rainy-weather cracking and disease.

The desire to put cherries under plastic has spurred demand for size-controlling rootstocks and precocious trees that can be planted much closer together, Cline said. Protective covers are being used from Norway to New Zealand, with many local innovations. New Zealanders put covers over frames built over tall trees, while Norwegians tend to lay the covers close to or on the trees.

Earnscy Weaver, from Summerfruit New Zealand, said covers have not been the total answer to cracking. Covering trees can lead to soft fruit and “they might as well be cracked,” he said. Growers are moving to smaller trees and retractable covers that are not over the trees all the time, so fruit maturation isn’t affected by reduced photosynthesis.

Growers are using calcium chloride, applied as sprays or by frost protection irrigation equipment, to offset the effect of rain.

“It does reduce cracking,” he said, and it results in firmer fruit, but it must be done as soon as rain starts. There is very little dose tolerance. It can burn leaves and reduce fruit luster.

The demand for sweet cherries is leading countries like Chile and New Zealand to find ways to get fruit to far-away markets. For both those countries, sweet cherries must survive 30 to 50 days on a ship and arrive in markets in good condition.

In Chile, Juan Pablo Zoffoli at Catholic University in Santiago studies the entire production chain, looking for critical points at which quality losses can occur. Chilean cherries need to stay fresh on a boat for up to 50 days.

The most common kinds of quality losses include pitting, internal browning, skin roughening, fruit softening and denting from contact, impact and compression bruising.

Cherry pickers are taught how to hold their fingers and hands and how to detach cherries from the trees and lay them into picking baskets. Hydrocooling times and durations are studied, as are the types of shipping bags, shipping temperatures, relative humidity and the balance needed between oxygen and carbon dioxide in the bags.

With fresh sweet cherries being lured to Europe and Asia from half a world away, it’s not surprising that U.S. growers are interested as well.

Bob Dailey, from Orchard View Farms in The Dalles, Ore., gave a report on the Oregon industry. It was a repeat performance. He gave a similar report five years ago.

“Everything is going to fresh,” he said.

Tonnage of Oregon cherries going into processing fell from 40,000 per year in the late 1990s to 21,000 last year, driven by economics, he said.

Growers get 40 cents to 50 cents a pound for brining cherries compared to a dollar and more for fresh market. The three important processors in Oregon are still processing, but they get their cherries from Turkey, South America, Eastern Europe and Michigan, while the Oregon cherries are going by boat to Southeast Asia, the United Kingdom and Taiwan.

“Everybody is planting more cherries,” he said.

Oregon, Washington and California combined are planting about 1.4 million trees a year and growers have to order them two to three years in advance. While half the cherries are Bing, he said, growers want both earlier varieties like Stella or later ones like Steena and Sweetheart.

Fewer than 20 percent are going in on dwarfing rootstocks, with growers sticking to Mahaleb and Mazzard.

The industry is consolidating into fewer, larger packers, he said.

The big challenge now is labor, he said.

“We are willing to pay for it, but we need it,” he said. “Returns justify it.”

The West pays minimum wages higher than most, $7.50 and more per hour, but the big fear is that a crackdown on immigration will occur with no provision for farm labor.

The United States is No. 3 in sweet cherry production, he said. Turkey is No. 1, and both Iran and China are potentially large suppliers.

Like Chile and New Zealand, the American West is focusing on cold chain management, maintaining quality during shipping and finding ways to operate orchards and packinghouses to maintain quality.

What about sweet cherries for processing – for ice cream ingredients and maraschinos, for juices? That will come from sorts from fresh market packing lines, he said.

Orchard View Farms currently raises 1,400 acres of sweet cherries and packs them for fresh market. The Bailey family has operated the farm for four generations.

Of the countries represented at the international program, only Italy seemed content to produce high quality sweet cherries but limit them to local markets. Davide Neri, from the University of Ancona, said Italian growers are mostly small producers who grow on diversified farms, using family labor, and enjoy good markets in Italy for two months starting May 20.

Land is at a premium in Italy, but growers have several attractive crops to grow, including olives, walnuts, apricots and kiwi, he said.

While many cherry orchards are large, old trees, new acreage is being planted in higher density on dwarfing rootstocks using a variety of training systems.