About one-sixth of California's raisin acres are harvested mechanically, according to a report from the U.S. Department of Agriculture.

A total of 31,483 acres—or 16 percent—of the state's total raisin-grape acres are harvested using machinery, according to the report.

Broken down, 14,604 bearing acres were planted on the overhead trellis management system, accounting for 8 percent of the state's total raisin-grape acreage.

Growers in Fresno and Madera counties have 41 percent and 36 percent, respectively, of the overhead trellis plantings.

Kern County growers have an additional 21 percent.

The overhead system gets its name from the trellis system tall enough for most men to walk under.

Midway through the growing season, workers cut selected canes to prompt the grape bunches to begin drying.

At the proper moisture stage, a machine runs under the criss-cross trellis system, using rubber fingers to knock the dried grapes onto a catch tray. The raisins are sometimes refered to as dried on the vine, or DOV.

Other mechanical harvesting systems include continuous tray, at 8.5 percent of the acres, and the southside, with less than 0.05 percent of the raisin-grape acres.

Fresno County also had the most mechanically harvested acres with 19,121 acres.

Most raisins bunches are hand cut, then placed on paper trays to dry. After several days, workers return to turn the partially dried grapes to ensure uniform drying.