Water Loss from Fresh Berries of Raisin Cultivars under Controlled Drying Conditions

Abstract

Traditional production of raisins by hand harvesting and drying grapes on paper trays is labor intensive and at risk to inclement weather. Dried-on-vine (DOV) raisin production uses mechanical harvesters and the risk of rain damage is reduced. Earlier-ripening raisin cultivars have been developed and released that are suited for this new production system. Raisin breeders would also benefit by knowing if there are differences in drying rates among cultivars. If raisin cultivars were both early ripening and had rapid dry rates, then they would be well suited for DOV raisin production. In a study over three seasons from 2002 to 2004, results showed significant differences among cultivars for drying rates. Summer Muscat, Diamond Muscat, and Primus dried the fastest and Thompson Seedless consistently dried the slowest. DOVine and Selma Pete were intermediate. Water loss was affected more by berry size than by Brix. Drying rate increased more by removing the epicuticular wax by a chloroform dip than by rubbing. Summer Muscat dried faster than Thompson Seedless even when wax was removed by chloroform or rubbing. Results indicate that skin characteristics in addition to epicuticular wax might play a role in the differences in raisin cultivar drying rate. There were large differences among cultivars in the amount of cuticle as compared to epicuticular wax. These findings show that breeding advances are possible in the development of raisin grapes with high drying rates.