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GRAPE GRO WING vintages, cognizant that each vintage year will present its own unique conditions and challenges. The winegrowers and winemakers of Napa Valley understand that they are fortunate to grow grapes and make wine in such favorable terroir. Wine- growers and winemakers work collabor- atively to ensure that their grapes meet the wine quality parameters and will vinify high-quality wines. This strategic alliance of winegrower and winemaker is a key component of the success or failure of a vineyard. This Goblet-trained zinfandel vineyard is spaced 10 feet by 8 feet. The vineyard is drip irrigated, although the drip line is not shown. tors. Dr. Mark Matthews reports, "Prior research has shown no effect of yield on wine quality." He also states, "Quality cannot be measured by a scientist because it is so subjective." Most viticulturists agree that for the ultra-premium wine market, small yields that are balanced with the vine's vigor result in superior wines. The Napa Valley average yield for Cabernet Sauvignon from 1986 to 2004 was 3.8 tons per acre. By contrast, the California average for Cabernet Sauvignon for this same period was 5.55 tons per acre. The Napa Valley climate allows for the full maturity of even late-ripening variet- ies like Cabernet Sauvignon and Cabernet Franc. For many years, harvest date was determined by measuring sugar, acid and pH. These measurements are still made today, but the winemaker also tastes the fruit to determine when to harvest. For red varieties, most winemakers look for ripe, intense flavors with supple tannin structure. They also want the grape seeds to be brown and mature. Bibiana Guerra describes an Australian research project about Syrah confirming that seed color is a good indicator of physiologically ripe berries, ready for harvest. A given vineyard may be harvested block-by-block or even sub-block-by-sub-block on different days, based upon the flavor profile of the fruit. Most ultra-premium fruit is harvested by hand. However, the mechanical har- 38 Wines & Vines nOVeMBeR 2011 vester technology is so advanced that a substantial amount of Napa Valley fruit is now machine harvested. Harvest is the culmination of grow- ers' efforts. Before and during harvest, the winegrower and the winemaker (sometimes one and the same) observe the conditions of the vines and determine how best to meet the winemaker's param- eters for the fruit. They observe condi- tions down to the level of the blocks and sub-blocks (precision farming), and the grower then adjusts the cultural practices accordingly, including irrigation, fertiliza- tion and canopy management. When harvest concludes, the wine- grower and winemaker focus on the wine to determine if modifications to the cultural practices would improve yields and quality. The grower then considers whether to adjust those practices in future Footnotes The grower and winemaker also constantly work together to improve their know-how and stay at the forefront of technology. They recognize, respect and appreciate that each winegrowing region of the world has its own valuable history, tradition, science and practices that may differ from those of the Napa Valley, and they remain open to learn and adapt their skills and practices to improve the quality of Napa Valley wines. This commitment to excellence has been evident in the Napa Valley for many generations, resulting in the well-deserved internation- al reputation that Napa Valley has long enjoyed. Richard Mendelson is a lawyer specializing in vineyard and wine law with the law firm of Dickenson, Peatman and Fogarty in Napa, Calif. He directs the Wine Law and Policy Pro- gram at the University of California, Berkeley, School of Law and is past president of the International Wine Law Association. Robert Steinhauer managed vineyard operations at Beckstoffer Vineyards from 1971 until 1979 and Beringer Vineyards from 1979 to 2004 and is now a viticultural consultant with and co-owner of Wineland Consulting LLC. He is a past president of Napa Valley Vintners and in 2008 received the Merit Award from The American Society for Enology and Viticulture. The authors acknowledge and thank Hal Huff- smith and Tucker Catlin for their peer review of this article. 1. A pruning trial conducted in Napa Valley utilizing Cabernet Sauvignon grafted to 110R rootstock resulted in significant differences in sensory attributes. That seemed to defy the conventional wisdom. The low yields of 1.74 tons per acre resulted in "veggie aroma and flavors, bell pepper aroma, bitter- ness and astringency," while the high-yield wines of 8.98 tons per acre were "higher in red/black aroma, jam aroma and fresh fruit aroma." Other research has pointed out the need to achieve balance between capacity (yields) and vine vigor. 2. A radiational freeze occurs when a cold but dry (low dew point) air mass moves into the valley. Tempera- tures can be in the 60°s (Fahrenheit) in the afternoon, but after sunset radiational cooling of the soil surface causes temperatures in the lower atmosphere to fall, sometimes by 30ºF or more. Temperatures a few hundred feet above the ground remain fairly constant, forming an inversion (temperature increase with elevation). 3. An advective freeze occurs when a cold air mass from the Arctic regions migrates into the Napa Valley. The temperatures at the vineyard are below freezing and become colder at higher elevations.