Napa Valley often gets unduly painted as a monolith of Cabernet Sauvignon, and, indeed, it grows a lot of it, with Cabernet making up 40% of the region’s total wine production and 55% of its value.
But despite Cab’s powerful presence, diversity exists. Many think first of cooler-climate Los Carneros when considering where Napa Valley’s non-Cabernet wines shine brightest. Yet when it comes to having a diverse range of grapes, Oak Knoll District of Napa Valley is both a living lab and a vital testament to diversity’s importance.
Oak Knoll is a cooler, southern-reaching area of Napa Valley, between the towns of Yountville and Napa. Long-standing producers based in the appellation, such as Robert Biale Vineyards and Trefethen Family Vineyards, have made the case for Oak Knoll wines made from grapes other than Cabernet Sauvignon for generations.
Jon Ruel, the CEO of Trefethen, says, “It’s a really special part of the Napa Valley, a sweet spot. There’s a real buzz about Oak Knoll District, but, as we are long on vineyards and short on wineries, people are excited about the fruit.”
The 8,300 acres (nearly 4,200 planted) that define Oak Knoll District stretch across Napa Valley’s widest point, from Redwood Road and Mount Veeder, on its western side, across Highway 29 to the Silverado Trail. Yountville borders to the north, and the southern boundary approximates the southern edge of the Dry Creek alluvial fan. The alluvial fan’s dominance was a crucial distinction in Oak Knoll District’s petition to the Alcohol and Tobacco Tax and Trade Bureau (TTB) to become an American Viticultural Area (AVA), a designation granted in 2004. Fine, gravelly clay loam, silt loam, and loam soils are well defined, as is the bedrock in the hillsides on the western edge of Oak Knoll, which exists alongside serpentine, sandstone, and shale. With a healthy watershed, Oak Knoll has a mix of soils that hold water well and cool the ground.
Because of its relatively low elevation, Oak Knoll is marked by a significant maritime influence from San Pablo Bay in the form of cooling breezes throughout the growing season and coastal morning fog, especially in summer. As a result, on comparable days, temperatures in Oak Knoll can be 10 degrees Fahrenheit cooler than those farther north in a warmer AVA such as St. Helena or Calistoga. This allows Oak Knoll grapes an extended ripening period, leading to soft tannins and bright acidity.
“We’re in a California coastal anomaly, where it stays cool even when the rest of the state stays hot,” Ruel explains. “Just warm enough for the reds, just cool enough for the whites. We couldn’t make an overripe Cabernet if we wanted to; we get New World ripeness and Old World freshness.”
Cabernet Sauvignon grows well in Oak Knoll, of course—this is still Napa Valley. But many other grapes do, too. Zinfandel, Chardonnay, and Merlot are widely planted. Altogether, more than 18 varieties are in production here, including Sémillon, Viognier, Syrah, Petite Sirah, and Meunier.
Oak Knoll’s history of grapegrowing dates to the 1850s. In 1852, at the height of the gold rush, Joseph W. Osborne brought vine cuttings from European grape varieties to his farm and planted a 50-acre vineyard, then the largest in Napa Valley. His property, Oak Knoll Farm, was named the state’s best farm by the California Agricultural Society just a few years later. Osborne was a contemporary of Agoston Haraszthy, who was busy planting Buena Vista, in Sonoma. Together, the two men created the Sonoma-Napa Horticultural Society. Osborne is credited with bringing Zinfandel to Sonoma through this association with Haraszthy. His contributions were curtailed when, in 1863, a former employee murdered him.
Oak Knoll Farm eventually became Eshcol Ranch, which included a wooden, three-level, gravity-flow winery built in 1886 and designed by Captain Hamden McIntyre, who also designed Inglenook, Greystone Cellars, Beaulieu Vineyard, Chateau Montelena, Frog’s Leap, and Far Niente. Eshcol, whose name is the Hebrew word for cluster, grew as the Napa Valley wine industry boomed around it. At one point, an estimated 50 grape varieties were planted on the property, from Chasselas and Riesling to Burger and Zinfandel.
By the turn of the century, however, the wine industry was suffering, largely because of phylloxera. During this dark period, which lasted through Prohibition, wine grapes were superseded by other crops. Excepting Prohibition, Eshcol produced wine until 1941. Beringer Vineyards then leased the vineyard and the winery for the next 15 years. In 1968, the Trefethens began to revive Eshcol. While restoring the property, they allowed Domaine Chandon to age its first wines on-site while Chandon was building its own winery on the western side of Yountville.
Today, Trefethen grows 10 varieties on 440 acres of estate vineyards and is among the giants of the region. Most of Trefethen’s grape acreage is planted to Chardonnay and Cabernet Sauvignon, but it also includes healthy amounts of Pinot Noir, Malbec, Riesling, Merlot, and Petit Verdot.
Trefethen uses only estate-grown grapes and maintains a full-time, year-round workforce, so having a range of grapes that ripen at different times helps balance the workload. Harvest, for example, typically extends for two and a half months. This model also helps the winery embrace regenerative practices; herbicides are never used, and Trefethen has made its own compost for 15 years.
“Diversity is important,” Ruel says. “It allows us to hedge our bets on the agricultural risks of frost and fire and spread the work out. We only get away with it because of the climate in Oak Knoll.”
Ruel admits that even Oak Knoll can sometimes be slightly too warm for some of the whites, so he must rely on both viticultural and cellar tools to make the best wines. He adds that, while there’s natural air-conditioning, he still—and increasingly—must be prepared for heat spells. Maintaining leaf coverage on the exterior of the grape clusters is one of the easiest ways to avoid sun exposure, especially from the brutal afternoon sun.
“For the Chardonnay, I do less than 5% malolactic fermentation, and for Chardonnay and Riesling, I pick some of it very early,” he says. “A less ripe white grape is not as complex, but it’s perfect for blending, with its citrus notes and acidity. The rest I pick later for complexity.”
The Biales first started making wine in Oak Knoll in the 1940s. Aldo Biale and his mother, Cristina, ran the family farm, just north of Napa, after the family patriarch died in a mining accident. With wine grapes in the agricultural mix, Aldo was young when he learned from relatives to make wine and quietly sold jugs of Zinfandel to his Italian neighbors.
In the 1990s, Robert Biale Vineyards became a legitimate wine business, with Aldo’s son Bob taking the reins. Bob remained faithful to the family’s roots, producing Zinfandel and other mixed blacks from old vine vineyards across Napa Valley and Sonoma County. But with a long-standing Oak Knoll winery and tasting room open to visitors, Biale is an important anchor in the region.
Bob Biale says, “There’s value in being connected to a voice and a source and an identifiable piece of land. People like those details.”
To expand the winery’s range, Biale tried making Sauvignon Blanc but felt it wasn’t all that distinguishable on its own and didn’t fit the family story. He wanted to grow an Italian white but wasn’t sure what would do well. His team tasted through 18 different varieties, and Greco di Tufo, a full-bodied white grape traditional to Campania, in southern Italy, was the hands-down favorite. In 2014, Biale planted one acre of the variety in the middle of his Oak Knoll estate vineyard, called Big Ranch, where a patch of Petite Sirah had been. The budwood came from UC–Davis by way of Steve Matthiasson, a winemaker and Oak Knoll District neighbor.
“We have a lot of the same degree-days as Campania,” Biale says. “We took an educated guess.” The guess was right. Biale and the estate’s winemaker, David Natali, ferment the wine in 95% stainless steel, with the remainder in amphora, concrete egg, and acacia. The first vintage was 2016. The TTB does not yet recognize Greco as an official variety, so the wine cannot be labeled as such. Instead, Biale calls it Clementina, to honor his mother.
Biale’s Oak Knoll Zinfandel is also from Big Ranch and is included in one of the winery’s most popular bottlings, Black Chicken. Budbreak happens later in Oak Knoll than in even cooler Carneros, and the soils are heavy and hold water well, cooling the ground and slowing ripening. Natali says, “We get density, color, plushness, [and] even ripening to flesh out the fruit a bit more. With Zin, we’re not waiting on tannin development.”
Biale also makes a Sangiovese from Nonna’s Vineyard, in Oak Knoll, the only 100% Sangiovese in the region. In 1993, the winery budded over older vines planted in the 1970s and kept one acre of dry-farmed Sangiovese.
“Sangiovese can be tough and tannic, but in Oak Knoll has a softer tannin profile,” Natali says. “The vines struggle, which makes for interesting fruit.”
Darioush farms 120 estate acres across the appellations of Oak Knoll and Mount Veeder. From Oak Knoll, it makes Shiraz and Viognier.
The Darioush winemaker Hope Goldie says, “I love the fruit here in Oak Knoll. We’re not fighting vigor; everything does well. The rich, deep soils provide enough cooling for acidity to develop, [and] they drain perfectly. I’d take Oak Knoll fruit any day for anything.”
Clif Family has 80 acres of organic-certified vineyards in Oak Knoll. The decision to buy land here was sparked when, in 2017, Stagecoach Vineyard was sold to E. & J. Gallo. Laura Barrett, the winemaker at Clif Family, made the case to the winery’s cofounders, Gary Erickson and Kit Crawford, that to be sustainable as a business, it likewise needed to own and farm more of its own land. Clif Family had just 10 acres across three vineyards on Howell Mountain at the time.
Clif Family was lucky to stumble across 40 fallow acres in Oak Knoll once owned by the Jaeger family, longtime grapegrowers in the area who were responsible, with the Trefethens, for planting the line of walnut trees along Oak Knoll Avenue between Highway 29 and the Silverado Trail.
Barrett says, “Oak Knoll was a sweet spot for us; we could plant so many things. And the site was a clean slate.”
Clif Family started by planting Chardonnay, Sauvignon Blanc, and Viognier. The latter of these was especially important, as Barrett couldn’t find Viognier grapes elsewhere in Napa Valley and had been making a popular version for years. Clif Family also planted Cabernet Sauvignon, Cabernet Franc, Merlot, Malbec, and Zinfandel with a regenerative approach, using sheep for weed control and designing vine rows for mechanization.
The winery had the chance to double down in Oak Knoll when an adjacent 40 acres—also planted organically, with a shared reservoir to tap—came up for sale. Barrett describes it as the right vineyard in the right place at the right time. This site is planted to Cabernet Sauvignon, Petit Verdot, and Petite Sirah, and some of the grapes are sold to other producers.
“Oak Knoll provides the opportunity for a lot of winemaker influence,” Barrett says. “It’s a long growing season. You can make a lower-alcohol Cabernet Sauvignon that is beautiful and delicate but not green—really nicely in balance. You can also extract and make a richer Cabernet. You’re more in control of either decision.”
She says things grow more slowly Brix-wise, the vines hold more fruit, and the soils are deep and hold water well, resulting in a bigger fruit load and more time to decide when to pick.
“We have balance in every vintage,” Barrett says. Compared with other areas in Napa, she explains, “it’s not as hot in the hot years or as cool in the cool years. It’s low risk—one of the reasons we wanted to be here. It’s a place where we can manage the highs and the lows.”
Barrett also loves the backbone of acidity that persists in Oak Knoll grapes. The reds can gain enough concentration and layering to be rich and fruity but retain acidity to age beautifully and remain fresh. For whites, Barrett says that she can make tart, fresh, searing versions of her wines or let the grapes hang a bit longer, yielding wines with more fruit and richness.
“It’s all there,” she says. “You’re able to fine-tune your acidity in the picking decision, always looking for flavor, but geek out with the numbers a lot more.”
The creativity that Oak Knoll winemakers can exercise is important, considering the uncertainties of climate change and increasing heat. The appellation offers not only a diversity of varieties but also the opportunity for diversity in wine style, and the acidity the region’s grapes can achieve provides freshness and vitality, which are attractive to modern consumers. This is the region’s time to shine.
Agoston Haraszthy and the Story of Buena Vista, by Kelli WhiteMW Perspectives: The Rise of Cabernet Sauvignon in Napa Valley from 1961 to 1976, by Ashley Hausman [Members only]Napa Valley Expert Guide [Members only]
Oak Knoll District of Napa Valley (website). Accessed May 4, 2023. https://www.okdnapa.com/.
Sullivan, Charles L. A Companion to California Wine: An Encyclopedia of Wine and Winemaking from the Mission Period to the Present. Berkeley: University of California Press, 1998.
Just a note about using the grape name Greco on labels.... 'Greco Bianco' is on the list of varieties that TTB has approved "administratively" but is not yet on the official Federal statute (27 CFR 4.91). There are several other grape variety names that are on the same 'approved, but not quite' list that are, in fact, already being used by wineries in the US (Pinot Bianco, Ribolla Gialla, Saperavi, Schioppetino, & more). I'm not sure exactly why Robert Biale feels they couldn't put Greco on the label. Penrose, Mathiasson, and perhaps others already use Greco on labels. Matthaiasson has even labeled theirs in some vintages as 'Greco di Tufo,' which would obviously be illegal to send to the EU and even legality under US law might be debatable.