Some of the clearest language about clones comes from Napa Valley vintner John Caldwell.
“In viticulture, a clone is a population of vines derived by vegetative propagation from a single vine, called a mother vine,” he says. “All vines grown from cuttings or buds of this vine are genetically identical. Future generations will remain identical unless a spontaneous mutation occurs, creating a bud with an altered genetic makeup.”
In addition to founding Caldwell Vineyard in the Coombsville appellation, which cultivates 10 clones of Cabernet Sauvignon, among other wines, Caldwell ran a certified California nursery from which he could legally sell vine cuttings. He was also the first American importer of French clones licensed by France’s regulatory agency, Etablissement National Technique pour l’Amélioration de la Viticulture (ENTAV).
Clonal selection began in Germany in 1926 with the goal of finding the best possible material to plant. The prevailing wisdom is for growers to plant a variety of clones and their own clonal selections to achieve complexity without obscuring terroir.
Currently, the practice occurs in wine regions worldwide. For Cabernet Sauvignon, it’s less of a focus than with Chardonnay and Pinot Noir, especially in the New World. But Cabernet clones still matter.
“Clones are real, but they are more a bookkeeping method of keeping track of what has less disease,” says M. Andrew Walker, University of California, Davis, department of Viticulture and Enology Professor Emeritus, and a grape breeder in the department for 30 years who recently retired. “Clones are not discernible from each other genetically. We can’t determine genetic distinctions [between clones], only organoleptic.”
As such, winemaker Jean Hoefliger keeps detailed notes on the Cabernet Sauvignon clones he prefers to work with across the world, zeroing in on the acidity and tannin levels of clones 4, 6, 7, 8, 15, 169, 337 and 338.
He divides them into ones that make what he considers to be juicier wines (169, 337, 338), against those that offer more in the way of structure and tannin (4 and 15). He looks at yield, at ripening timeline and ultimately at the profile of the fruit that results, preferring most of all to have the right mixture of clones.
“I look at clones the way I look at coopers,” he says. “I don’t want too much of one. It’s like going back to the old days of field blends, looking for diversity and complexity, but bringing the diversity on purpose.”
Diversity without disease is central to clones’ importance.
In the 1930s and 1940s, it became clear that virus diseases like leafroll were reducing both the productivity and quality of vineyards in California, as detailed by Deborah A. Golino, the director of Foundation Plant Services (FPS), and James A. Wolpert in Wine Grape Varieties in California, a publication of the University of California.
Back then, many of the commercially available grapevine selections were mislabeled or incorrectly identified. This led UC Davis Professor of Viticulture and Enology Dr. Harold Olmo to form the California Grape Certification Association in 1952 to develop, maintain and distribute virus-tested grape stock that was also correctly identified.
By 1958, that program merged with UC Davis’s fruit and nut tree program to become the Foundation Plant Materials Service, now known simply as FPS. It maintains the Foundation Vineyard, where grape varieties are registered and certified and then sold to nurseries as “certified stock,” meaning they have been rigorously tested for viruses.
FPS also imports new grape selections from around the world, adding to the diversity of clones, and works to preserve clones growing in premier vineyards, including selections from older vineyards that represent pre-1900 European introductions.
ENTAV has contributed significantly to the diversity of clonal material, as has the Geisenheim Research Institute in Germany and Vivai Cooperativi Rauscedo in Italy. Some clones are trademarked and/or proprietary, though many others are in the public domain.
Still, the choice of clone is only one of many important decisions that go into planting a vineyard.
“Variety choice, site climate, soil type, vineyard design (spacing, trellising and rootstock) and annual cultural practices (irrigation, canopy management and crop load) will impact final wine quality far more profoundly than clonal choice,” write Golino and Wolpert in Wine Grape Varieties in California.
Cabernet Sauvignon is one of the most widely planted Vitis vinifera cultivars in the world, a cross between Cabernet Franc and Sauvignon Blanc that is associated with high-quality and ageworthy wines. It is grown globally, most notably in the Bordeaux region of France and in California’s Napa Valley. Australia, Argentina, Chile and Washington State also grow a sizable amount of Cabernet Sauvignon.
FPS counts more than 60 distinct clones for Cabernet Sauvignon, many of them proprietary and many authorized from ENTAV in France, meaning they cannot be distributed without permission from the owner.
Clones 7 and 8 are considered the two workhorse clones in California, both sourced originally from the Concannon Vineyard in Livermore, founded in 1883. The Clone 7 selection was made in 1965 and known first as Superclone #101. Clone 8 and Clone 11 also originated from Concannon in 1965.
Clone 6 is a highly regarded selection from the former University of California Foothill Experiment Station in Jackson, but tends to offer lower yields than 7 and 8.
Clone 2 is another notable one, first known as the Oakville selection and selected by Dr. Olmo. According to FPS, the Kunde Estate in Sonoma Valley was planted in the 19th century with imported cuttings from Chateaux Margaux and Lafite Rothschild in Bordeaux. Dr. Olmo developed that selection from Kunde at Larkmead Vineyards in Calistoga in the 1950s, where he consulted, and at the U.C. Davis Experiment Station in Oakville.
Other transparent lineages include Clone 63, which came originally from the nursery at Hermann J. Wiemer Vineyard in the Finger Lakes region of New York. It was later propagated at Stagecoach Vineyard in the Napa Valley and remains proprietary to that vineyard.
Also in the Napa Valley, Spottswoode Estate Vineyard has its own proprietary clone, Clone 51.
At Chimney Rock in the Stags Leap District, General Manager and Winemaker Elizabeth Vianna bottles a Clone 4 Cabernet and a Clone 7 Cabernet, separating each to showcase its charms. Clone 4 is originally from Mendoza, Argentina.
Her Clone 4 vineyard is on the northern edge of the estate, mature and low-yielding with small berries. The resulting wine is intense. Clone 7, on the other hand, is one of two mountainside vineyards on the property, also on the northern edge, steep and planted in shallow volcanic soils. That wine is muscular and bright.
“The morphology of the cluster, tannin levels and fruit profile all vary by clone and clonal diversity on our estate has really broadened the picture we can paint of Cabernet Sauvignon through our single-vineyard wines,” says Vianna. “Clone 4 has the tiniest berries on the property.”
Other California Cabernet Sauvignon clones of note include Clone 24 from the Laurel Glen Vineyard in Sonoma County, selected in 1988, and Clone 30, the Heritage Disney Silverado clone from Stags Leap District and one of three well-respected Cabernet Sauvignon clones selected by Phil Freese and Deborah Golino in 1989. This one is from a vineyard off the Silverado Trail near the Napa River believed to be planted with the See clone of Cabernet. Additionally, Clone 31 is the Heritage Mondavi clone also selected by Freese and Golino in 1989, this one from a 50-year-old vine in To Kalon Vineyard.
“I think if you are a Cabernet winemaker and you are planting vineyards and growing your own fruit, it is absolutely essential to think about clones,” adds Vianna. “Fine-tuning clone and rootstock combinations and also thinking about site where each is important can really impact quality. This is when Cabernet starts to get really thought-provoking.”