Zinfandel, long called a "mystery grape" because it seemed to appear from nowhere in California Gold Rush days, hyped by a promoter named Agoston Haraszthy, who claimed that he had brought the rare grape to California from his native Hungary. In fact, Haraszthy certainly exaggerated his role: Zinfandel (sometimes rendered "Zinfindal," "Zierfandler" or "Zeinfindall") was well-known in the Eastern U.S. as a table grape long before Haraszthy set foot in Napa. It had turned up in a horticultural fair in Massachusetts as early as 1834.
Also, based on similarity in the grape and its leaves and the wine it made, Zinfandel for many years was thought to be a sibling of the Southern Italian Primitivo of Puglia.
It was only as recently as 2001 that modern grape sleuths, including Dr. Carole Meredith of the University of California at Davis, used DNA technology to confirm that Zinfandel and Primitivo are the identical grape, albeit different clones; and the same is true of the little-known Crljenik Kasteljanski of Croatia, which is now thought to be the original variety, exported to Italy as Primitivo and to the U.S. as Zinfandel.
Based on this evidence, the European Union moved quickly to permit Italian producers to use either "Primitivo" or "Zinfandel" to label wines made from either grape. The move makes great sense for Italy, as Zinfandel is immensely popular in the U.S. and more likely to sell wine exports than the relatively unfamiliar Primitivo.
U.S. regulators, on the other hand, have been slower to approve legal changes. The name Primitivo is now permitted for U.S. wineries (such as Rabbit Ridge) making wine from the Primitivo clone; but in contrast with European rules, American wineries may not use the names Primitivo and Zinfandel as synonyms. A proposal to allow this has been on the books since 2002 but has not been acted upon, reportedly because of opposition by Zinfandel producers who aren't excited about the possibility of competition.
Meanwhile, because the U.S. has signed off on the European labeling laws, this results in a curious situation in which European wineries may call Primitivo "Zinfandel" in U.S. sales, but American wineries may not.Frankly, and probably more because of differences in wine-making styles than in fruit or terroir, Primitivo and Zinfandel are not all that similar. There's often a berry-like character in both, but differences typically fall across the usual Old World-New World lines, with most Zins landing on the big fruit, high-alcohol side, while Primitivo tends to lower alcohol and hints of earth, plus a whack of oak if the producer wants to impress the critics.