Effects of Berry Size and Crop Yield on Wine Composition and Sensory Quality

The effects of vine irrigation and crop yield on sensory quality of Cabernet Sauvignon wine from the 2000 harvest were investigated using descriptive analysis with a trained panel, quality ratings by members of the wine industry and tannin assays.Wines produced from vines with low irrigation regimes were rated highest in dried fruit/raisin, jam, and red/black berry aromas, fruity by mouth, and acidity and lowest in brown color. The high irrigation wines were rated lowest in bitterness, ethanol, body, and darkness. The medium irrigation wines were ranked highest in veggie aroma, astringency, brown, dark, body, ethanol, and bitterness and were ranked lowest in cherry aroma. Low irrigation wines received slightly higher quality ratings from members of the wine industry than high irrigation wines, but the difference was not significant, possibly because of differences among wine replicates.Lower crop yields tended to produce wines with high bell pepper and black pepper aromas, high astringency and bitterness, and high ethanol and veggie by mouth flavors, whereas the higher yields tended to result in wines with higher red/black berry, jam, and cherry aromas, red color, fruity by mouth, and acidic characters. Tannin concentration was significantly higher in the wines produced from low crop yields, consistent with the higher bitterness and astringency ratings given to those wines by descriptive analysis.We continued our investigation of the effects of crop yield on wine sensory quality using pruning and thinning trials on Cabernet Sauvignon grapes harvested in 2001.In the pruning trial, six treatments that left 12 to 48 buds/vine at pruning were imposed for the second consecutive season on the same vines. Vines were pruned to variations of 1 to 4 bud spurs and shoot thinned accordingly. These treatments resulted in 24 to 60 clusters/vine and produced yields that varied almost 2.5 times from lowest (3 tons/acre) to highest (8 tons/acre). In addition to yield components, a number of vegetative growth parameters were measured including budbreak, shoot diameter, and shoot length. There was only a slight decrease in shoot diameter, but shoot length was a strong inverse function of bud number, varying about 100%from highest to lowest bud number per vine. The cluster weight did not differ significantly among treatments. Although berry size was not constant among treatments, the differences were not greater than about 10%and did not show any clear relationship to the crop loads.In the thinning trial, vines were pruned to 2 or 4 bud spurs that were then cluster thinned at veraison to create 8 different crop load treatments. Crop load in this cluster thinning experiment was well distributed among the 8 thinning treatments, varying about 4-fold from 4 to over 16 lbs. per vine. These crop loads correspond to yields that vary from about 2 tons/acre to about 8 tons/acre. Thus, we were more successful in accomplishing low yield by cluster thinning than by severe pruning. There were 14 replicated yield treatments, six for the second year and eight for the first time in 2001. Wines were made from each treatment, and they are ready for bottling and subsequent sensory and chemical analysis this spring.