Limerick Lane Vineyards’ old vines in Sonoma County. (Limerick Lane Vineyards/Limerick Lane Vineyards)

“You can’t find wines like these anywhere else in the world but California,” Chris Cottrell proclaimed to anyone who would listen — or at least, anyone with an outstretched hand holding a wine glass. Cottrell, partner in the Bedrock Wine Company, was pouring samples of Evangelho Heritage Red, a single-vineyard wine from Contra Costa County made primarily from zinfandel, at one of several crowded tastings during the annual Zinfandel Experience in San Francisco in January.

Cottrell was preaching the gospel of zinfandel. His statement was nearly identical to what his business partner, Morgan Twain-Peterson, told me three years earlier when I visited Bedrock Vineyard in Sonoma Valley. Yet in the context of “ZinEx,” as the three-day event was colloquially called, the statement seemed almost as defensive as celebratory. Zinfandel, after all, has a bit of an identity crisis.

Zinfandel’s uniqueness stems from two factors: its status as California’s grape, without an Old World paradigm like cabernet sauvignon to Bordeaux, or pinot noir and chardonnay to Burgundy; and the “old vine” vineyards scattered throughout California, which give the wines a romantic connection to the frontier days. The trade group Zinfandel Advocates and Producers, or ZAP, which sponsors ZinEx, was formed in 1992 to promote and preserve these distinctions. (And, well, to fight the then-prevalent misconception that zinfandel is a white grape.)

But those old vineyards aren’t entirely zinfandel. Vintners knew there were other varieties mixed in, such as alicante bouschet, petite sirah, mataro (a Spanish name for mourvedre) and carignane. But DNA testing, a science that has developed dramatically over the past 20 years or so, has identified many more varieties and determined that zinfandel is actually the minority in some of these vineyards. Yet the wines are often better than 100 percent zins.

Zinfandel clusters tend to ripen unevenly, so the wine has a peculiar ability to taste underripe and overripe at the same time. The immigrant farmers, mostly Italian, who planted those vineyards in the late 1800s and early 1900s understood that a diversity of grape varieties would produce a stronger, more cohesive wine. Some would add color, tannin and structure for endurance. Some would ripen early and be a hedge against harvest rains, while late-ripening varieties would contribute depth in good vintages.

The DNA science also took zinfandel on an Ancestry.com-style quest for its roots in Europe. And like those people in the commercials who find out they aren’t really who they thought they were, the results were surprising. Zinfandel was determined in the 1970s to be identical to the primitivo grape of southern Italy. (Primitivo is now considered to be a distinct clone of the variety.) The search then turned to Croatia, where an initial identification with a grape called plavac mali turned out to be false. Subsequent testing finally identified zinfandel as an obscure Croatian grape called tribidrag. It’s no longer in commercial production in Croatia, and no wonder. Who wants to order a glass of tribidrag? We’ll stick to zinfandel, thank you. (Though Carole Meredith, the now-retired University of California at Davis professor who led the DNA quest, does call her zin as tribidrag on her Lagier Meredith label.)

Meanwhile, back home in California, the founders of ZAP had a quandary. Those old vineyards can be spruced up and restored to health, but they can’t last forever. Nurseries lacked high-quality plant material for new zinfandel vineyards. So along with the Viticulture and Enology Department at the University of California at Davis, ZAP created the Heritage Vineyard Project in 1995. Cuttings from old-vine vineyards throughout California were planted at Davis and later in Oakville, in Napa Valley. The original 90 selections were whittled down to 20 that were virus free. Of those 20, four were selected to represent heritage zinfandel — from the Moore, Teldeschi, Zeni and Lytton vineyards. These selections were planted in experimental “heritage” vineyards around California, and their cuttings are available to growers planting new vintages.

“The differences among the four selections are subtle,” says Joel Peterson, founder of Ravenswood Winery and one of the most famous zin producers. (He is also Twain-Peterson’s father.) And the differences seem to be dependent on where the vines grow. “We now know how zinfandel expresses itself and the important role site plays in that expression.”

The answers aren’t yet definitive. “We believe the Heritage Vineyard Project is 20 years into a hundred-year effort,” says Rebecca Robinson, ZAP’s executive director. “Our goal is that zinfandel will thrive for many more generations, even though the original vineyards will one day be a distant memory.”

There’s also a style question: Zinfandel tends to be high in alcohol. If it’s not made carefully, the burn from the alcohol can overwhelm the fruit. Tradition-minded producers strive to make a restrained “claret-style” zin. Producers of this style to seek out include Bedrock, Carlisle, Limerick Lane, Robert Biale, Ravenswood, Ridge, Frog’s Leap and Peachy Canyon.

The heritage zinfandels will never be able to replicate the old-vine vineyards. Just as successive generations of immigrant families become more American while preserving elements of their heritage, these vineyards will evolve zinfandel’s expression. All the more reason to enjoy the wines we have now.