Submitted to: American Society of Enology and Viticulture Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: March 2, 2007
Publication Date: June 19, 2007
Citation: Ramming, D.W. 2007. Water Loss from Fresh Berries of Raisin Varieties under Controlled Drying Conditions. American Society of Enology and Viticulture Annual Meeting Abstracts. Technical Abstract: The standard raisin variety, Thompson Seedless, ripens late and is not well suited for cane cutting and drying-on-the-vine for mechanical harvest because special trellises are needed to improve drying and supplemental drying after harvest may be needed. Early-ripening raisin varieties have been developed that dry quickly when canes are cut so supplemental drying is not necessary after harvest. Different drying rates have been noticed in field trials of newly introduced raisin varieties compared to Thompson Seedless. Drying rates under controlled conditions for new raisin varieties need to be determined to see if there are differences due to berry characteristics; not cluster or vine characteristics. Fresh berries of Thompson Seedless, Summer Muscat, Selma Pete, DOVine, Diamond Muscat and Primus were harvested in three separate growing seasons (2002, 2003, 2004). These varieties were separated into two berry diameters (12.7 and 14.3 mm) and each berry diameter separated into three sugar levels (20, 22, 24 ±1.8 oBrix). Four replications of 5 berries per treatment were dried at 52oC (2002) and 38oC (2003, 2004) for 7, 13 and 19 days respectively. In 2003, additional treatments of removing the wax from the surface of the berries by rubbing with Kimwipe tissue or chloroform dip for 15 seconds were applied to Thompson Seedless and Summer Muscat. For the three seasons studied, there was no significant difference between water loss for berry size, however, there was a trend for small berries to loose water more rapidly. Berries with 20 oBrix had significantly higher water loss rates than 22 and 24 oBrix, with 24 oBrix being the lowest. There were significant differences between variety water loss rates within the different years. Summer Muscat had the highest water loss except in 2003 when it had the second fastest water loss rate. Thompson Seedless had the lowest water loss rate except in 2004. Initially it was intermediate in water loss but by day four it had the lowest water loss. Summer Muscat had been observed to dry faster in the field when canes were cut than DOVine, even though Summer Muscat had lower sugar levels. This shows that the varieties’ berry characteristics do influence water loss rates differentially. The removal of the berry’s surface wax with chloroform increased the water loss rate by up to 2.5 times compared to the control. Removal of the wax by wiping was not as effective as the chloroform treatment for increasing water loss rates. However water loss was significantly greater than the control. Even with the removal of wax, there were still significant difference in water loss between Thompson Seedless and Summer Muscat, possibly associated with the cuticle and skin thickness as well as pore number and size.