Crop Yield and Vine Irrigation Effects on the Sensory Quality of Vitis vinifera L., cv., Cabernet Sauvignon and Sangiovese Wine.

This Ph.D. dissertation examines the effects of vine pruning, crop thinning, and vine irrigation on Cabernet Sauvignon and Sangiovese wine sensory attributes.. Descriptive analysis was used to examine the differences among wines made from multiple pruning, thinning, and irrigation treatments. In addition, a new SPME GC-MS method was developed to quantify 2-methoxy-3-isobutylprazine, a vegetative aroma compound, in wine. For the yield experiments, Cabernet Sauvignon vines in the Napa Valley were subjected to 6 winter pruning treatments over two vintages and 8 cluster thinning treatments over one vintage, with thinning imposed at veraison. The treatments created yields that varied from 4.3 to 22.2 t/HA. In addition, 5 thinning treatments were imposed on Sangiovese vines in the Pope Valley, creating yields that varied from 17.2 to 39.8 t/HA. In general, vegetal attributes decrease in intensity and fruity attributes increased in intensity as bud number and yield increased. In contrast, there were few sensory differences detected in the wines made from the cluster thinning treatments, although the yield range was greater in the thinning experiments than in the pruning experiment. We concluded that wine aromas and flavors respond to yield manipulation, but do so significantly only when yield is altered early in fruit development. For the irrigation experiments, Cabernet Sauvignon vines in the Napa Valley were subjected to three irrigation treatments: minimal irrigation, 32 L water/vine/week, and 64 L water/vine/week. The treatments created yields that varied from 15.0 to 21.7 t/HA. The minimal irrigation treatment resulted in lower leaf water potential readings throughout the season. Wines made from the minimal irrigation treatment were rated significantly higher in fruity aromas and flavors than wines from the irrigated treatments. The standard irrigation treatment wines were rated significantly higher than the minimal irrigation treatment wines in vegetal aromas and astringency. We conclude that minimally irrigated vines lead to more fruity aromas and flavors in the resultant wines than irrigated vines. A newly developed 2-methoxy-3-isobutylpyrazine (MIBP) assay was used to quantify MIBP concentrations in the experimental wines. MIBP concentrations were significantly negatively correlated with buds per vine and significantly positively correlated with sensory vegetal intensity ratings.