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.