Effect of Viticultural Practices on Flavor Formation in Grapes

Norisoprenoids are volatile secondary metabolites which are important aroma constituents of a number of grape and wine varieties. The norisoprenoids are thought to arise from carotenoid breakdown and occur in grapes as glycosidically bound precursors. However, the factors which influence carotenoid breakdown and norisoprenoid formation in grapes are not well understood. In this study we evaluated the effect of seven levels of sunlight exposure (5%, 20%, 27%, 37%, 50%, 70%, and 100%, expressed as percent of full sun exposure) on norisoprenoid concentrations in three grape varieties (Chardonnay, Sauvignon blanc, and White Riesling). Our results suggest that viticultural practices which affect fruit exposure to sunlight may influence norisoprenoid composition of grapes and wines. In White Riesling, TDN (l,l,6-trimethyl-l,2-dihydronaphthalene) levels increased at sunlight exposures above 20%.