Scott Frost, Danielle Fox, Tom Collins, Markus Keller, and James Harbertson*
*Tufts University, Robinson Hall 212 College Ave, Medford, MA 02155 (scot.frost@tufts.edu)

Several reports from wineries suggest that Cabernet Sauvignon wine produced from fruit harvested after an early frost will have rose-like aromas. These aromas are described as atypical by winemakers and the affected wines are termed “rose tainted” or “frost tainted.” Anecdotal evidence suggests that inclusion of freeze-killed leaf material into the fermentation is the taint source. We investigated these claims by studying how adding leaf matter into the fermentation affects the chemical and sensory profile of Cabernet Sauvignon wine. Freeze-killed leaves were hand-collected from Cabernet Sauvignon vines in the Columbia Valley, then crushed and added to Cabernet Sauvignon must at four addition rates: 0.0, 0.5, 2.0, and 8.0 g/kg. A detailed analysis captured the treatment impact on the flavor and chemical profile of the experimental wines. The addition of freeze-killed leaf matter significantly increased the intensity of floral aroma, herbaceous/straw aroma, artificial fruit aroma, and floral aftertaste, while decreasing the dark fruit aroma and astringency. Gas chromatography mass spectrometry identified 66 volatile organic compounds (VOCs) that varied by treatment. Statistical analysis was then used to identify which com- pounds drive the changes in floral aroma, floral aftertaste, and astringency. Partial least squares, correlation, and fold-change analysis were then used to ascertain four marker VOC: 1,1,3,5-tetramethylcyclohexane, 6-methyl-5-hepten-2-ol, p-menth-1-en- 9-al, and 6-methyl-3,5-heptadien-2-one. Additionally, the phenolic composition of wines fermented with added freeze-killed material showed reduced concentrations of anthocyanins, tannins, and iron-reactive phenolics. These results clearly show the impact of freeze-killed leaf matter on Cabernet Sauvignon wine and provide convincing evidence of the taint source.

Funding Support: Washington State University, Auction of Washington Wines and all Washington grapegrowers and wineries through the Washington State Wine Commission