L. Peter Christensen

Yield, Quality, Sensory Attributes, and Consumer Acceptance of Seedless Muscat Raisin Grapes Dried on the Vine Or on Trays

Summary Goals: The California raisin industry is transitioning from tray-dry to dry-on-vine (DOV) production methods. Grapes dry more slowly on the vine compared to on trays, so the DOV method works better with raisin grape varieties that ripen earlier than Thompson Seedless. Earliness allows drying to commence during a hotter part of the summer, and affords a longer drying period. Summer Muscat and Diamond Muscat are among the earliest ripening of the newer raisin varieties, but they have not been widely planted, partly due to a lack of information about yield and quality, and also because of industry concerns that consumers would not accept their muscat flavor. Therefore, we conducted field research to document yield components and quality grades in Summer Muscat and Diamond Muscat, and we performed sensory and consumer acceptance tests to compare these varieties with Fiesta, a standard neutral-flavored DOV variety. Further, we considered whether the tray or DOV drying method affected consumer acceptance of raisins from these varieties. Key Findings: Diamond Muscat and Summer Muscat were similarly productive, with grapes that could fully dry on the vine, producing raisins with high “B or better” and low “substandard” grades. Both muscat varieties produced a high proportion of fruit from basal nodes, especially when trained to quadrilateral cordons. Fruit from basal buds is undesirable for cane-pruned DOV varieties, so bilateral cordon training is recommended. Compared to Summer Muscat, Diamond Muscat had a higher proportion of “head fruit” (clusters on renewal shoots and below the point where canes were severed), and Diamond Muscat berries were heavier and less acidic. Compared to tray-dried raisins of a given variety, DOV raisins were less brown and more homogeneous in color, smaller and less homogenous in size, had finer wrinkles, and were spicier, sweeter, less sour and astringent, and less chewy than tray-dried raisins. Grapevine variety and drying method interacted to affect consumer preference in raisins; consumers most preferred Fiesta raisins (tray and DOV) and Summer Muscat raisins dried on trays, and they least preferred Summer Muscat DOV raisins. Impact and Significance: We found that Diamond Muscat and Summer Muscat have similar and high productivity, sufficient earliness to ensure consistent and adequate drying, and reliably good quality scores, making both varieties well suited for DOV raisin production from an agronomic perspective. However, consumer acceptance of Summer Muscat raisins was strongly affected by drying method; the DOV method resulted in the least-liked raisins in the study, and the tray drying method produced the most-liked raisins. In contrast, drying method did not strongly affect consumer preference of raisins from other varieties, although drying method consistently affected many of the tested hedonic variables.