Frozen Leaf Material Causes “Frost Taint” in Cabernet Sauvignon

Abstract

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 termed to be “rose tainted” or “frost tainted.” Anecdotal evidence suggests that the inclusion of freeze killed leaf material (FKLM) into the fermentation is the source of the taint. We have investigated these claims by studying how the addition of FKLM into the fermentation affects the chemical and sensory profile of the resulting Cabernet Sauvignon wine. Freeze killed leaves were hand collected from Cabernet Sauvignon vines in the Horse Heaven Hills; then crushed and added to Cabernet 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 freezing temperatures prior to harvest. A detailed analysis was performed capturing the treatment impact on the flavor and chemical profile of the experimental wines. Gas chromatography mass spectrometry identified 60 volatile and semi-volatile organic compounds that were correlated with the FKLM addition. Additionally, the phenolic chemistry showed reduced concentration of anthocyanin, tannin, and iron reactive phenolics. Descriptive sensory found that the addition of FKLM significantly increased the intensity of floral aroma, herbaceous/straw aroma, artificial fruit aroma, and floral aftertaste, but also decreased the intensity of dark fruit aroma and astringent mouthfeel. We estimate that ~3 freeze killed leaves per vine will produce the taint characteristics. Overall, these results clearly show the impact of freeze killed grape vine leaves on Cabernet Sauvignon wine quality and provide convincing evidence of the taint source.