Over the past several years we have made significant progress toward improving our understanding of vegetal aromas in wines, particularly in the varietal Cabernet Sauvignon. Our studies indicate that experts (i.e., winemakers) use many different criteria to classify wines as vegetal. Although there is some consistency among winemakers in the use of vegetative terminology, similar aromas may all be categorized together (Objective 1). Descriptive analysis with trained panelists indicated that trained panelists are able to distinguish among different qualitative differences within the overall category of vegetal terms (Objective 2). Therefore when communicating information about vegetal aromas, care must be taken to ensure that the terminology is well-defined (Objective 1 and 2). While methoxy pyrazines (e.g., 3-isobutyl-2-methoxypyrazine, IBMP) are frequently associated with bell-pepper character, other compounds may also play an important role in vegetal aromas (Objective 3). Interactions between vegetal and fruity aromas can serve to mask perception of vegetal aromas in some cases (Objective 2). In addition, interactions with matrix components such as polyphenols and tannins may result in decreased flavor volatility and perception (Objective 2). Viticultural practices can influence IBMP levels and sensory perception of vegetal aromas. However, growing region, row orientation, and vine microclimate all interact in complex ways to influence composition and sensory properties (Objective 4).
Using a solid phase micro extraction (SPME) procedure combined with GC-chemiluminescence detection we have validated a method to measure volatile sulfur-containing compounds in wines (Objective 3). During the past year we also completed sensory studies (descriptive analysis) and chemical analyses on Cabernet Sauvignon wines made from a cluster thinning trial (Objective 4). In general, the differences yielded by the cluster thinning treatments did not show any clear associations between any of the yield components (yield per vine, number of clusters per vine, number of berries per cluster, and berry weight) and fruit and wine composition or sensory attributes. The experiments were done in a high-vigor site and warm climate (Oakville, Napa Valley, Region III), therefore it is possible that environmental conditions may have also played an important role in final chemical and flavor properties of Cabernet Sauvignon, mitigating the potential impact of cluster thinning.
During the 2001-2002 funding year we obtained wines and associated viticultural information from industry cooperators. A graduate student was hired and has been coordinating these efforts. Sensory studies have been initiated and are expected to be completed by the end of the funding year. A GC-O-MS instrument was purchased, has been installed at UCD, and preliminary method development and validation has begun. Descriptive analysis of wines made from a wide range of Cabernet Sauvignon viticultural trials has begun. The completed analysis will act as a screening tool, identifying potentially important viticultural parameters meriting further systematic study.