A quest to find the best zinfandel clones began in the early 1990s, wrote Ann Hanami of the Napa Valley Wine Examiner. UC Cooperative Extension viticulture specialist James Wolpert was getting feedback from winemakers about the poor quality of the four available commercial zinfandel clones from the Central Valley, whose main characteristics were high-yield, large berries and poor varietal character.

Wolpert went on a California “safari” to find old-vine selections that had evolved uniquely over time on their own home turf. With support of Association of Zinfandel Advocates...