After trying mechanical raising harvesting on his 50- to 80-year old raisin grape vines for the first time last year, Jim Berekoff has gone back to hand picking and laying the grapes to dry by hand this season.

The harvester, he discovered, was too hard on the older vines and he says last year’s mechanical harvesting experiment contributed to a big yield loss this year.

Berekoff Farms grows 60 acres of Thompson seedless grapes for raisins and another 70 acres for juice near Kerman, Calif., using a single wire trellis system. This year’s week-long hand harvest of the grapes for raisins began Sept. 1. Harvest of the younger, mechanically-picked juice vineyard started about a week later.

“The younger vines can handle the beating of the mechanical harvester,” Berekoff says. “But, because of their age and the sandy and sandy-loam soils, the machine ‘rearranged’ a lot of the older vines. If I continued mechanically harvesting them, the machine would have kept damaging them enough to knock them over.”

Poor pre-harvest cane cutting to start the drying process was another reason for the lower production this season. Besides leaving too few canes for the 2009 crop, the cutting removed runners used for replants.

This year, he compared yields from the 40 acres of mechanically picked raisin grapes last season with an adjoining 20 acres of grapes that were hand picked.

“This year, that hand-picked field produced more than 2.5 tons per acre,” Berekoff says. “But, we’ll be lucky to pull 2 tons per acre out of the field where the harvester ran.

“Last year, machine picking saved me about $350 to $400 per acre, compared to harvesting by hand. But, if I damage the vines and tonnage goes down the next year, it’s not worth it.”

While production of his raisin grapes this year is down overall from 2008’s unusually large crop, Berekoff is pleased with their quality. At the start of harvest, his tests showed a little over 21 Brix and an acid level just under 6 pH.

He uses a conservative approach in measuring sugar levels. “I usually test the greenest, heaviest sections of the vineyard where sugar is usually lower,” he explains. “I like to pick when I get 21 in those areas. That way, I know the sugar in the rest of the grapes will probably be higher.”

Berekoff attributes the good quality year to ideal growing season weather. “We didn’t have any unseasonably hot or cold temperatures or long stretches of hot days,” he says. “The warm days and cool nights helped the grapes sugar up better. This will be a nice raisin crop.”