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New DOV raisin production system offers considerable promiseNew DOV raisin production system offers considerable promise

Harry Cline 1

November 4, 2008

8 Min Read

It was a cool, cloudy and overcast Saturday morning with rain showers in California’s Central San Joaquin Valley.

It was perfect weather for a field day to demonstrate a new mechanically-harvested dried-on-the-vine (DOV) raisin production system.

The early October gathering drew about 50 growers, packers, consultants and bankers to a three-year-old vineyard near Fowler, Calif. Boghosian Raisin Packing Co. hosted the event billed as a look at the “new raisin economy.”

It featured one of only two extra side mechanical grape harvesters shaking DOV raisins from vines in a vineyard planted to a new, well-adapted DOV raisin variety trellised like a table grape vineyard.

It is the newest wrinkle in an industry-wide effort to get away from heavy dependence on hand labor to gather and sun-dry raisins and to avoid early fall damaging rain and foggy weather.

It has taken as many as 50,000 workers two months to pick, spread out on paper trays, turn, roll and gather nature’s ultimate candy — sun-dried raisins. All this is concentrated within a 60-mile radius of Fresno, Calif. Therefore, the threat of a weather disaster is large with such a concentration.

With the growing shortages and increasing costs of labor, growers, packers and viticulture researchers have been on a two-decade-long quest to find ways to sun dry grapes quicker either on the ground or on the vines and mechanically gather the dried fruit.

There has been considerable progress. Industry observers estimate at least 50 percent of the Valley’s raisin crop is either dried completely or partially on the vine and then mechanically picked up. The most common method involves growers cutting canes holding green fruit to begin the drying process and then harvesting with a mechanical grape harvester onto continuous paper trays laid between the vine rows where the drying is completed. It takes about two weeks to dry raisins on a paper tray, but the drying period is dependent on the weather. The dried raisins are then gathered by pickup machines and deposited into gondolas or wooden bins.

The mechanically harvested/continuous tray system is popular because it can be adapted to existing vineyards without major vineyard re-trellising or retraining existing vines.

When the industry began its quest to perfect the DOV system, a major focus was on a closed-row arbor system low enough so workers could walk under the rows to work without reaching too far above their heads. It has been fairly widely adapted for new vineyard plantings.

Grapes hang down over rows. When grapes reach desirable sugar levels, canes intertwined on trellis wires are cut and the grapes dry on the vine. However, it requires special low profile equipment to farm and harvest these grapes since the rows are arbored over. Conventional tractors and sprayers will not fit underneath the continuous canopy.

These vineyards are very high producing, according to David Parrish, chief executive officer of A&P Structures, a leader in developing the pancake/arbor system and other trellising systems for all grapes. Raisin yields easily double and can more than triple traditional yields from the time-honored method of picking and drying the grapes on paper trays between vine rows. “You can produce 7.5 to 8 tons of grapes in the pancake top system. However, the problem is you may not be able to dry that many tons because there is no sunlight getting to the raisins,” Parrish says. “If you wind up having to dehydrate seven tons at $400 per ton, you lose money. Chances are every three years you are going to have to do some dehydrating with the arbor system.”

He adds that the pancake/arbor system must be installed in large blocks of 40, 80 or even 100 acres to be economical for a grower. It is not practical to convert an existing vineyard into an arbor system.

The gable system demonstrated at the field day was one Parrish said he developed 25 years ago for table grapes. “It is basically a South African gable system opened up in the middle.” It dramatically increased table grape yields.

A 5-foot wide metal V is positioned atop a 6-foot grape stake. There are eight wires on the V because of the tonnage potential in the system Parrish adapted to DOV raisin production. The Boghosian V-gable vineyard where the field day was held has a 12-foot wide row spacing and 5 feet between plants down the vine row.

“The number of wires is also related to keeping canes stable in the trellis system after they are cut to dry the grapes into raisins. If the canes do not remain in the trellis, they end up piled in the harvester or gondolas. You don’t want that because it increases your labor costs to take canes out of the harvested raisins and clogging up the harvester,” Parrish says.

Also, the eight wires keep canes separated in the spring through the season. If high winds then bunch up canes, that means grape bunches would grow too close together, increasing disease issues as well as inhibiting drying.

Parrish says, however, the first step in developing the gable system was not the trellising. It already existed. The starting point was the mechanical grape harvester. For this he worked with Tom Thompson, president of AGH, Fresno, Calif.

Together they developed a wider harvester with the same V-shape in the straddle-row harvesting mechanism as the V trellis. Thompson says the typical wine grape harvester is 24 to 36 inches wide — “42 inches at most.” For the gable trellis, it needs to be 60 inches, said Thompson.

There are only two AGH harvesters that are that wide, but Thompson says he expects more to be developed.

“With the price of raisins now, growers can afford to look at developing new raisin vineyards with the trellising system developed by A&P,” Thompson says.

Or they can slowly redevelop an existing vineyard.

“That is what makes this gable system more attractive to growers because they can convert an existing vineyard to this and do it themselves a few acres at a time,” said Parrish. “When you plant a vineyard with an arbor system, it has to all be put in at once in a relatively large block. That is expensive.”

The most obvious advantage to the gable system over the pancake system is that it can be farmed with conventional vineyard equipment and the grapes can be harvested green for the juice or wine market if a grower does not make raisins.

It is not cheap. Parrish said it costs about $4,600 for the V-gable system. However, it is $900 per acre less than the pancake-arbor system.

The third element that makes the V-open gable more attractive is a variety that is more adaptable to it than the traditional Thompson seedless raisin vineyard.

It is the Selma Pete variety. “I had this variety in mind when we started developing the V-gable system,” explains Parrish.

Selma Pete was developed by USDA-ARS breeder David W. Ramming and technician Ronald E. Tarailo at the Kearney Ag Center in Parlier, Calif. The variety was named after longtime UC viticulturist L. Peter Christensen, who spent many years successfully developing DOV growing practices.

Selma Pete is far more adaptable to DOV raisin production than Thompson, says Parrish.

“Selma Pete does not throw out laterals. It is a strong vine that better handles cane cutting to dry the grapes than Thompson. It does not mind being at a flatter angle than a Thompson. It does not wimp out when it is flat, and enough sunlight gets into the canopy to develop buds for the following year’s crop,” Parrish says.

In most DOV systems, growers are producing grapes for one season and renewal canes and buds for the next season on the same vine. It requires careful winter pruning and crop management to ensure consistent production year after year.

Parrish said a major breakthrough in the DOV process came from now retired University of California Tulare County Viticulture Farm Advisor Bill Peacock.

Peacock developed the idea of alternating fruit-producing vines with vines producing renewal wood every other year rather than developing renewal canes and fruit on the same vine.

“Bill Peacock’s idea was a major breakthrough. It made the DOV system simpler, and it reduces pruning costs,” Parrish says.

Philip Boghosian, owner of Boghosian Packing, farms both pancake/arbor and V-gable vineyards. Harvesting costs with the V-gable system are only 10 percent to 15 percent that of hand harvesting.

“The grapes are hanging in the air, off the ground to dry. There is reduced risk of mold if it rains. No imbedded sand issues with DOV grapes,” he says, adding that the chance of a food contamination issue is greatly reduced when the grapes are kept off the ground during drying.

“The move to mechanical harvesting will only continue to grow,” he said, adding that the mechanically harvested/continuous tray system has been a breakthrough for the industry.

“I like to think of the continuous tray system as a bridge between harvesting and the gabled-V system we demonstrated at our field day,” Boghosian says.

“Hopefully, we will see more field days like the one we hosted, so not only growers, but packers and bankers really understand the breakthroughs of what we can do to produce high quality raisins,” he concludes.

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