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Oak Knoll AVA

by David on June 29, 2009

Locals often refer to the Oak Knoll District of Napa Valley as a “sweet spot”, referring to its amiable climate. Because of the mild weather, this small area (about 3500 plantable acres in an 8300-acre area) is home to more than a dozen different grape varieties.

In 1850, a former sea captain and horticultural enthusiast named J.W. Osborne purchased 1800 acres of land a few miles south of Yountville and called it Oak Knoll. Part of this historic site later became the Eschol Winery (1886) and is the current site of Trefethen Vineyards. He established a very large nursery and was the first to plant wine grapes in the Oak Knoll region. Among his many horticultural projects, he made it his personal mission to replace the insipid and ubiquitous Mission grapes that made most California wine at the time, with better varieties. Zinfandel was one of these “better varieties” and he is believed to be one of the key players responsible for bringing it from the east coast to the Napa and Sonoma valleys for the first time. This was a momentous event because Zinfandel quickly became the most widely planted variety in California, and remained so until prohibition. By 1860, Osborne’s 50-acre vineyard was the largest in the Napa Valley. If his work hadn’t been cut short by an untimely death (murdered by a disgruntled employee) in 1863, he would probably have been called the father of Napa Valley wine.

With this kind of history, it’s surprising that the region hasn’t had formal recognition from early on. In the 1990s, the growers and vintners of the district began making their case to the federal government, compiling information from soil experts and engineers, meteorologists and historians, and the Oak Knoll District finally gained AVA status in April of 2004. As with all AVAs, the minimum requirement is 85% Oak Knoll grapes to put the Oak Knoll AVA on the label (see GCU article “What is an AVA?“).

It should be noted that its official name is “The Oak Knoll District of Napa Valley” in order to differentiate it from the Oak Knoll Winery in Oregon. For the purposes of this article, we’ll refer to it as the Oak Knoll District or AVA.

Over a dozen wineries make their home within the Oak Knoll AVA and about 40 others regularly purchase grapes from growers within the region, including some of Napa Valley’s most prestigious Chardonnay producers. The observation is that the mildness of the climate produces whites that are restrained and elegant in style, yet there’s enough warmth for later-maturing Bordeaux varieties to ripen slowly, yielding graceful, fruit-forward wines of soft tannins. The cool conditions keep the Cabernet yields down, but most producers find the quality and character of the wine offsets the low production. The principal varieties of the region are Merlot, Chardonnay and Cabernet Sauvignon. Viognier isn’t a widely planted grape variety in the Napa Valley, but the mild conditions and well-drained soil in our mid-district vineyard are ideal for it and give a tremendous perfume to our Goosecross Estate Viognier.

The Oak Knoll District is bordered by the Mount Veeder AVA to the west, the Yountville District to the north and the Carneros District to the south. Of the 14 Napa Valley AVAs (as of July, 2006) the Oak Knoll District is clearly the most regionally consistent in terms of soil and climate. The uniformity of climate is due to the broad, flat, almost exclusively valley-floor topography. There is a great deal of marine influence from close-by San Pablo Bay, moderating the temperatures with morning fog and whipping up cooling afternoon breezes on the warmest days of the growing season. It’s second only to Carneros as Napa’s coolest AVA, with small pockets of an even cooler climate on the lower foothills along the western and eastern borders.

The uniformity of soil owes itself to the very large Dry Creek alluvial fan, which is the defining feature of the region. Centuries ago the Diablo and Haire series clay it once had in common with the neighboring Carneros District was buried by alluvial deposits from San Pablo Bay, Dry Creek and the Napa River. Repeated flooding and recession left deposits of loam, fine, gravelly clay loam and silt loam, setting it apart from its neighbor to the south. This fan spreads out over most of the district and the only deviation is a bit of volcanic soil in the northwest part of the district, some visible bedrock along the western border and some sandstone, shale and serpentine in the hillsides, making way for colorful clay toward the bottom (the district is almost completely flat).

Thus far, in 2006, it’s still somewhat uncommon to find a wine with the newly-created Oak Knoll AVA designation on the label, but as more and more of them are released, we expect the wines to express their place of origin through great fruit structure and gentle, elegant tannins. A sweet spot, indeed!

Regional statistics (with thanks to the Napa Valley Vintner’s association):
Temperatures: growing season high: around 92°F (31.5 C); low: 50°F (10C)
Elevation: sea level to 800 feet (244m), most areas at just above sea level
Rainfall: 36 inches (90cm) annually

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