Final Report June 2023
Principal Investigator: James Harbertson, Washington State University, Richland
Cooperators: Tom Collins, Washington State University, Richland; Markus Keller, Washington State University, Prosser
Summary: This research sought to investigate claims by wineries that Cabernet Sauvignon wines made from fruit that was picked after an early frost had occurred, had “rose-like” aromas. A team of WSU researchers investigated these claims by studying the impacts of frost on leaves chilled in controlled chambers and by making wines with chilled and dead leaves added prior to fermentation. After conducting two experiments comparing chilled leaves and frozen dead leaves, it was concluded that frozen dead leaves were necessary for the off-character to be detected in wine.
Results from the sensory study showed that additions of 2 g/per kg of must or greater were necessary to have a perceivable increase in floral attributes. A model solution experiments of Chardonnay and Cabernet Sauvignon grape leaves showed that marker compounds identified in frost tainted wine were extracted in both aqueous and model wine frozen leaf extracts in a short period of time (24-hours). This suggests frozen leaves present in the fermentation can result in these off-aromas and that alcohol is not required for this to occur. Pre-cursors (carotenoid breakdown products) to terpenoid-like aromas (2,3-dihydro-4-methyl-furan, (Z)-3,7-dimethyl-1,3,6-octatriene, geranyl acetate) were also found in the aqueous and ethanol extracts of frozen leaves suggesting that yeast metabolism or reactions occurring during wine aging may contribute to the formation of additional frost taint aroma markers.
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