Ongoing research of Sunpreme raisins is exhibiting some positive results for their potential as a commercially produced variety. Growers were recently updated on the progress of the variety at the 2018 San Joaquin Valley Grape Symposium in Easton.
“The yields look pretty good and the quality I think is also very good,” said Matthew Fidelibus, Extension Specialist with the Department of Viticulture and Enology at UC Davis. “I brought some raisins to the meeting and people have been trying them and everything I’ve heard has been positive.”
Research trials are being conducted to determine the best production method for the variety, which illustrates significant promise for a substantial reduction in labor. “The vines can be pruned by machine and then the dried raisins can be harvested by machine,” said Fidelibus.
Traditional dried-on-vine varieties require workers to cut the stems above clusters of grapes to initiate the drying process before being mechanically harvested. Sunpreme raisins are different in that the variety “dries naturally after ripening, so the fruit just ripen and then they start drying, so there’s no cutting needed,” Fidelibus stated.
The data collected also illustrated some issues with the variety, with fruit falling off the vine at levels of roughly ten percent and another ten percent falling during the harvest. However, Fidelibus noted that “even after those losses, we achieve a pretty respectable yield, similar to the dried-on-vine we have now with cane pruned varieties.”
Along with examining the performance of Sunpreme raisins using different rootstocks, Fidelibus has been evaluating the most effective trellising technique at the UC Kearney Agricultural Research and Extension Center. Fidelibus and his team have been looking at “optimizing the trellises for machines to make sure that we can take the best advantage of the opportunities that this new variety offers in terms of being able to machine prune and machine harvest.”