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

Abstract

<h3>Background and goals</h3> 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 considered “rose-tainted” or “frost-tainted.” Anecdotal evidence suggests that the inclusion of freeze-killed leaf material (FKLM) in the fermentation is the source of the taint. <h3>Methods and key findings</h3> 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. Gas chromatography-mass spectrometry identified 60 volatile and semi-volatile organic compounds that correlated with FKLM addition. Additionally, the phenolic chemistry showed reduced concentrations of anthocyanin, tannin, and iron-reactive phenolics. Descriptive sensory analysis found that adding 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. <h3>Conclusions and significance</h3> We estimate that approximately three freeze-killed leaves per vine will produce taint characteristics. 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.