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The Cienega Valley in San Benito County is the only place in the world known to have a significant planting of Cabernet Pfeffer, a wine grape also known as Mourtaou.

Vineyard owner Pat Wirz once considered ripping out his century-old Cabernet Pfeffer vines because no one wanted to buy the fruit. Now he’s got a waiting list of winemakers eager to get the grapes.

San Benito County is not known widely as a wine destination. But this sparsely populated area near Monterey is the global epicenter for a certain type of wine that’s quickly, and improbably, gaining attention: Cabernet Pfeffer.

The Cabernet Pfeffer grape (no relation to Cabernet Sauvignon, confusingly) can produce a wine that’s light, perfumed and peppery, precisely the sort of fresh, chillable red that’s so in vogue right now. Increasingly, top California winemakers are competing for access to the 15 or so acres of Cabernet Pfeffer that were planted more than a century ago in San Benito County’s Cienega Valley — likely the largest concentration of Cabernet Pfeffer acreage in the world.

“It’s a rural, parochial remnant of a very isolated region in California that only now people are rediscovering in some weird way,” said Morgan Twain-Peterson, winemaker at Bedrock Wine Co., which makes a varietal Cabernet Pfeffer wine and also uses it in a red blend.

The grape is also shrouded in mystery. No one knows how the plant material got to Cienega Valley from its native France, nor how exactly it got its name. Until recently, in fact, no one knew for sure what it was. Theories abounded: It was a genetic crossing of the grapes Trousseau and Cabernet Sauvignon. No, it was actually a synonym for the Bordeaux grape Gros Verdot. No, it was a catchall term for a field blend of multiple grape varieties. It’s been called Manseng, Pinot St. George and a host of other names.

Cabernet Pfeffer vines, planted in 1903, at the Wirz Vineyard in Hollister (San Benito County).

Those theories have all been put to rest now, thanks to genetic testing performed by UC Davis showing that Cabernet Pfeffer is one and the same as Mourtaou, a grape from southwestern France that’s all but extinct in France now. Yet the folktales persist. “It is Mourtaou,” said Kobza Wines owner Ryan Kobza, the winemaker who submitted the plant material to UC Davis for testing. He finds it frustrating that people keep entertaining the other theories, especially the Cabernet Sauvignon-Trousseau hypothesis.

Even if its origins are understood, Cabernet Pfeffer nevertheless continues to offer plenty of mystery. As to how it was imported from France in the late 19th century, why it was planted only in the Cienega Valley and how 15 acres of it managed to endure more than a century’s worth of trials including Prohibition — no one has a definitive answer.

The mystery, no doubt, has added to its allure in a moment when California’s historic wine grapes are all the rage. The wackier the story, the cooler the wine seems. But unlike some antique viticultural curiosities, this one in fact makes quite a delicious wine.

“Every few years someone tries to revive a ‘heritage grape,’” said winemaker Josh Hammerling of Berkeley’s Hammerling Wines. “Often it’s just novelty. This one actually tastes good.”

Pat Wirz, owner of the Wirz Vineyard, shows the first buds of the year that have appeared on his Cabernet Pfeffer vines.

Everyone agrees on a couple of Cabernet Pfeffer facts. In the late 1800s, a German immigrant named William Pfeffer owned a grapevine nursery in Saratoga. Also around that time, the grape was planted in the Cienega Valley. Four plantings have survived, at the vineyards now known, respectively, as Enz, Wirz, Gemelli and DeRose.

But how is Mr. Pfeffer connected to the Cienega vineyards? It’s reasonable to assume that the nurseryman might have named one of his products after himself, or that people would have referred to grapevines purchased from him by his name. Is it a coincidence that Pfeffer is German for “pepper,” which happens to be the prevailing flavor of the wine? And how did “Cabernet” get mixed up in it?

Pat Wirz, owner of the Wirz Vineyard, whose 5 acres of Cabernet Pfeffer were planted in 1903, believes that Mr. Pfeffer was friendly with another German immigrant known as Dr. Orwall, who owned what’s now the Gemelli Vineyard. “But I don’t know which one of them imported the cuttings from France,” Wirz said of the two Germans. Whether Mourtaou ever had a meaningful fan base in Europe is likewise unknown.

The whole thing sounds like a long, convoluted game of telephone, making for ripe conditions for spurious theories. The plant’s leaves resemble those of Trousseau, a red grape from France’s Jura region, which may explain the longstanding Cabernet-Trousseau crossing theory. And some genetic tests from the late 1990s and early 2000s, predating the Mourtaou match, did actually return false results. One turned up a probable match for Gros Verdot, a Bordeaux grape variety. (This is likely because Mourtaou’s genome was not added to the UC Davis database until relatively recently, so it may have shown matches with grapes that are genetically related, but not identical.)

The farmers who grew Cabernet Pfeffer in the Cienega Valley in those early years were probably not obsessing over its identity. For them, its appeal would have been clear: Unlike Mission, the wine grape that dominated in California until the late 19th century, Cabernet Pfeffer is easy to grow and easy to make into wine. The vine’s loose clusters make it resistant to mildew. Its yields are generous. The fruit holds on to color and acid well even in hot conditions — suggesting that it could be especially useful as California’s climate warms. And its structure lends the wines a chemical stability that Mission often lacked. “It probably checked a lot of boxes of what people were looking for when they made California ‘Burgundy’ or ‘claret,’” said Twain-Peterson.

Or maybe its planting in Cienega wasn’t quite so calculated. “We’ve got to be careful not to ascribe too much thought process to things that were going on in the Wild West,” said Ian Brand, who will release a Cabernet Pfeffer from the 2020 vintage. “A lot gets lost in translation.”

Bottles of Cabernet Pfeffer, also known as Mourtaou, a wine grape found almost exclusively in California’s San Benito County.

There was a time when Wirz considered pulling out his vines, he said, since he couldn’t get winemakers interested in buying the fruit. The only reason that winemakers got interested, about eight years ago, was because they wanted to buy Wirz’s Riesling grapes. “I was there for the Riesling, but Pat was really excited to show me this Cab Pfeffer block,” said Nicole Walsh, who started her Ser wine label in 2014. “I was skeptical. I’d never heard of it. But I said OK, Pat, I’ll take some.”

The Wirz Cab Pfeffer has since become Ser’s flagship wine.

It may have taken 120-odd years, but the style of wine that Pfeffer naturally delivers is finally popular. If the market once rewarded dark, concentrated, hefty reds — the prototypical California Cabernet Sauvignon — it’s now come around to lighter, translucent, more delicate options. Santa Cruz winemaker Ryan Stirm said his Cabernet Pfeffer is now reliably his fastest-selling red.

Many of its fans compare the grape to Nebbiolo, an Italian variety that produces savory, light, brick-colored reds with formidable tannins. When talking to his customer base at his Berkeley tasting room, Hammerling describes it as “something like a semi-carbonic Gamay or Trousseau,” terms now familiar to natural-wine acolytes. Cab Pfeffer wines are dependably full of red-fruit flavors like strawberry, cranberry and pomegranate, and many winemakers employ carbonic maceration — a fermentation technique that tends to bring out a fruit-candy note.

More than anything, though, the Cabernet Pfeffer signature is the pfeffer itself. “It’s a very distinct white pepper for me,” said Walsh. “Not the black pepper you get in Syrah. Every vineyard has its own expression, but I always get that white pepper.”

Pat Wirz, owner of Wirz Vineyard, removes weeds from the area around his vines in Hollister (San Benito County).

Now, Wirz has more winemakers interested in the fruit than he can accommodate. Every winemaker interviewed for this story said they’d like to get more Cab Pfeffer grapes than they currently receive. Luckily, the acreage is expanding, albeit modestly: The Gemelli Vineyard planted an additional 7 acres this year, Kobza said. That would increase the Cienega Valley’s total Cabernet Pfeffer acreage by over 25%.

“I know it’s not from California, but it’s been isolated for such a long time to one little part of California that I would say it is Californian, in a sense,” said Kobza. “In the context of this long, unfinished story, it seems like there’s a possibility that it may really grow substantially in the next 10 years.”

Esther Mobley is The San Francisco Chronicle’s senior wine critic. Email: emobley@sfchronicle.com Twitter: @Esther_mobley

Wines made from Cabernet Pfeffer - or Mourtaou, as some winemakers prefer to call the variety - tend to be light and translucent in color, showing delicate flavors of red fruit and spicy pepper, but with a backbone of firm tannins. All of the wines listed here express that general profile, but each has its own idiosyncrasies. Note: These wines are all from San Benito County's Cienega Valley. Lime Kiln Valley, where Enz Vineyard is located, is a sub-appellation within the larger Cienega Valley American Viticultural Area.

Ser Cabernet Pfeffer Enz Vineyard Cienega Valley 2018 ($40, 13.4%). Maraschino cherry, strawberry candy, white pepper.

Stirm Cabernet Pfeffer San Benito County 2020 ($33, 12.9%). Earth, dusty tannins, wildness.

Tessier Mourtaou Siletto Vineyard San Benito County 2021 ($38, 11.53%). Cranberry, bubble gum, plum.

Hammerling "The Wild One" Cabernet Pfeffer Enz Vineyard Lime Kiln Valley 2020 ($29, 12.9%). Spice, bing cherry, violets.

Kobza Mourtaou Wirz Vineyard Cienega Valley 2018 ($22, 13%). Cracked pepper, mushroom, iron.

Bedrock Cabernet Pfeffer Enz Vineyard Lime Kiln Valley 2020 ($48, 13%). Perfume, cranberry, grippy tannins.

DeRose Cabernet Pfeffer Cienega Valley 2018 ($40, 14.5%). Ripeness, currant jam, cedar.

Senior wine critic Esther Mobley joined The Chronicle in 2015 to cover California wine, beer and spirits. Previously she was an assistant editor at Wine Spectator magazine in New York, and has worked harvests at wineries in Napa Valley and Argentina.