Unripe Berries and Petioles in Vitis vinifera cv. Cabernet Sauvignon Fermentations Affect Sensory and Chemical Profiles

Abstract

Petioles, rachis, and leaves are all matter other than grape (MOG), and although originating from vines, they potentially contaminate primary fermentations of red grape must. Fruit contaminated with high levels of MOG may be downgraded or rejected at the winery; however, management practices such as hand harvesting or fruit sorting may reduce MOG. Petioles are the most common form of MOG to be included in the must, yet little is known about their chemical composition and resulting effects on the sensory and chemical properties of red wines. A descriptive analysis panel (n = 12) examined the sensory profiles of Cabernet Sauvignon wines to which 0.5% or more of MOG (petioles or unripe berries) had been added. This sensory analysis showed that an addition of 10% petioles to the must had a perceived impact on sensory wine qualities, increasing floral aromas and reducing bitterness relative to the sensory qualities of control wines, and resulting in a fuller body than that of wines made with unripe (i.e., green) berries. These sensory results are related to increased terpene concentrations as petioles increase in concentration in the wine must. Methoxypyrazines can also be detrimental contaminants to Cabernet Sauvignon wines. Concentrations of the predominant methoxypyrazine in the wines, 3-isobutyl-2-methoxypyrazine, increased with increasing additions of unripe berries to the must. Wines made with 0.5% or more of unripe berries during fermentation were associated with increased perceived acidity in the sensory analysis and an aroma that was more leafy and vegetal green than the aromas of some wines made with added petioles. The results of this study provide winemakers with important information to better understand how grape-harvesting choices may affect the perceived quality and chemical composition of their wines.