Harvest Seminar
The Oak Knoll District
[Page 1 of 4]
Saturday, October 14, 2006
Trefethen Vineyards
1160 Oak Knoll Avenue, Napa
60,000 case production
The fragrance of must filled Napa Valley the morning Wine Library members assembled outside the winery at Trefethen to embark on a visit to the fourteenth American Viticultural Area (AVA) in Napa Valley, Oak Knoll District (OKD). Jon Ruel, Trefethen Vineyards’ Director of Viticulture, joined by David Whitehouse, its Vice President of Winery and Vineyard Operations, gave an overview of both OKD and Trefethen, as the last of its Dijon clones of Chardonnay were being picked and crushed.
OKD was approved in 2004. At the southern end of the Valley, it is cooled by a marine layer of air off San Pablo Bay. Oakville is warmer than OKD and Carneros, cooler. Fog along its rivers means cool mornings. OKD has no one soil type (unlike Rutherford with its Rutherford Dust). Trefethen estate vineyard soil is derived from Dry Creek alluvial fans--thrown rock and gravel. Aerial views reveal old riverbeds expressed in overarching vineyard canopies. Trefethen also has a mix of loam, clay and clay-loam soils, perfect for a variety of wine groups. Jon called OKD a "sweet spot" for growing wine grapes. Its Chardonnay is planted at the cool end of OKD, Pinot Noir at the warm end of that variety (although there are a few Rutherford Pinot vineyards), and Cabernet at just its southern [cool] limit in Napa Valley.
Presently, there are 2,500 planted acres in OKD, twenty bonded wineries, with over seventy-five other wineries that buy OKD fruit. More Merlot is planted than Chardonnay. Jon said Merlot is not as picky about microclimate and does fine in clay. Trefethen has 425 acres of estate vineyard. It grows Cabernet Sauvignon (25 acres of which is hillside), Pinot Noir, Chardonnay, Merlot, two blocks of Riesling, Viognier (available only at the winery), Petite Verdot, Malbec, and Cabernet Franc and makes only estate wines. It sells about 35 percent of its fruit to other buyers. Most of the Pinot Noir is sold to Schramsberg, Mumm and Chandon (Chandon first crushed at Trefethen). Fifteen Chardonnay clones and ten rootstocks provide a diversity of aromatic profiles and ripening times. The Malbec ripens very early, one week ahead of the earliest Merlot. The Cabernet, planted on gravel, is at the cool end of its growing limits and requires thoughtful viticulture, care in vineyard development and soil analyses. Gravelly soil’s quick drain means quick mathematics. Stressful soils limit crop levels, as well as barley and rye cover crops, which can compete and slow down the vines’ growth. Six tons an acre on hillside is all right for Cabernet and other Bordeaux varieties and four tons an acre on the flat. This July, foothills three miles away were five degrees warmer. Fog keeps OKD temperatures down on the Valley floor. The Chardonnay is at its warm end for planting. Its viticulture has to take in sunburn but, thankfully, there is a lot of fog. Trefethen thins heavily for easier ripening. Chardonnay is pruned vertical shoot position (VSP) for exposure and because of multiple heat spells. Summer is the time for pulling leaves for specific presentations. One or two leaves are left outside for diffuse dappled light on the cluster; more leaves are left inside. Each vine is visited eight times from pruning to picking. Trefethen maintains a full-time vineyard crew of 55.
In the old winery, upstairs among wines aging in barrels, Trefethen had Wine Library members taste its Chardonnay. The 1868 winery was designed by H. W. McIntyre (who also designed Far Niente and Greystone-CIA). [Trefethen was once part of Captain J. W. Osborne’s extensive Oak Knoll farm.] In 1968, the Trefethens bought the winery and vineyard along with prunes and walnuts. The 1970’s replant was part of a renaissance in Napa Valley, replayed in the 1990’s because of phylloxera. Aging of wines continues in the original winery building while fermentation takes place in a new building next door. Originally, wine fermented in open top redwood tanks on the bottom floor, after horses powered the crush on the top floor and presses on the middle. (Dave said the aging was probably done in San Francisco.)
Jon called the 2004 Trefethen estate grown OKD Napa Valley Chardonnay vibrant with great fruit flavor--tropical, citrus. Trefethen limits yeast participation in fermentation by allowing some yeast in oak, some in stainless, 100 percent ML in some, less in others--25 percent overall. Different toast levels contribute to flavor as well. No more than 25 percent new French oak, 80 percent barrel and 20 percent tank fermentation give the pineapple and grapefruit flavors. Dave called acid backbone the key to winemaking.
26 vineyard blocks means 26 different lots to ferment. Trefethen grows two Chardonnay types: UC Davis Olmo clones 4, 5, 8 and 14 keep acid better in warm environments (California is warmer than France); and the popular Dijon clones 76, 96 from Burgundy. Irrigation ten to fifteen years ago was patch by patch on the 425 acres. Now there are 121 valves, 20 soil moisture probes and daily pressure bomb testing to monitor 400,000 vines. Jon can compute the gallonage per vine. With afternoon breezes off San Francisco Bay, OKD can be even cooler than Carneros and Chardonnay harvest later because of a longer growing season. Trefethen irrigates Chardonnay, so the fruit can hang until flavors fully develop. Chardonnay blocks are picked with sugar levels as low as 21° and as high as 24° to 25° Brix. By withholding Cab irrigation, smaller Cabernet berries give more skin, less pulp. And, with cool nights, the acid stays there. Water used in irrigation is reclaimed from winery operations as well as conserved winter rainfall. Jon finds vineyard sustainability increases as quality increases.
