Freeze-Killed Leaf Material Causes Atypical Aromas and Astringency in Cabernet Sauvignon

Background and goals Washington State Cabernet Sauvignon wines made from fruit harvested after an autumn freeze have been shown to present potpourri, floral, and rose-like aromas. These aromas are described as atypical by Washington State winemakers and the affected wines are con-sidered "rose-tainted" or "frost-tainted." An-ecdotal evidence suggests that the inclusion of freeze-killed leaf material (FKLM) in the fermentation is the source of the taint.Methods and key findings Freeze-killed leaves were hand-collected from Cabernet Sauvignon vines in the Horse Heaven Hills, then crushed and added to Cab-ernet Sauvignon must at four addition rates: 0.0, 0.5, 2.0, and 8.0 g/kg. The Cabernet Sauvignon fruit was not exposed to freez-ing temperatures prior to harvest. Gas chro-matography-mass spectrometry identified 60 volatile and semi-volatile organic com-pounds that correlated with FKLM addition. Additionally, the phenolic chemistry showed reduced concentrations of anthocyanin, tan-nin, and iron-reactive phenolics. Descriptive sensory analysis found that adding FKLM significantly increased the intensity of flo-ral aroma, herbaceous/straw aroma, artificial fruit aroma, and floral aftertaste, but also de-creased the intensity of dark fruit aroma and astringent mouthfeel.Conclusions and significance We estimate that approximately three freeze -killed leaves per vine will produce taint char-acteristics. These results clearly show the impact of freeze-killed grapevine leaves on Cabernet Sauvignon wine quality and provide convincing evidence of the taint's source.