(SFChronicle) - Wines can get better with age. Do vineyards?

The term “old vine” is one of the last unregulated terms that you’re likely to see on a wine label. Though I’ve never found an example of blatant misuse — no one is slapping “old vine” on a vineyard they planted last Tuesday — “old” is nevertheless relative. A label that says “old vine” could equally refer to 30-year-old vines (especially in a younger wine region) or to 150-year-old vines. So how old is old?

Justice Potter Stewart’s famous axiom holds up here. “I know it when I see it,” laughs Mike Officer, owner of the 89-year-old Carlisle Vineyard in the Russian River Valley and a co-founder of the Historic Vineyard Society, which keeps a registry of old vineyards. He’s right. Vines of a certain age look almost like a different plant species — not only because of their gnarled shapes and enormous girth (like a tree, a vine’s diameter increases with age), but also because vineyards were laid out quite differently a century ago. You won’t see those familiar tight, uniform rows of trellises, but rather erratic fields of heterogeneous, twisted growths, sparsely scattered, held up not by wires or stakes but by their own contorted mass. Bulbous, surreal and menacing, they call to mind Snow White’s haunted forest.

But the more interesting question than what’s old is whether, and in what ways, a vine’s age determines wine quality.

“I don’t know if we can say that old vines are better,” says Tegan Passalacqua, who makes wine from old vines for Turley Wine Cellars and Sandlands. “But I think they’re more stable.”

Young vines, like young people, are often vigorous to a fault. “They set more fruit than they can ripen,” Passalacqua says. As they age, vines learn to self-regulate. Yields come into balance, and grapes ripen more evenly. Older vines often produce smaller berries, which can lead to more structured wines; there’s a greater ratio of tannin-packed skin to juice.

That many of California’s old vines have always been dry farmed (irrigation was not a thing in the 19th century) amplifies their extreme root depths. “Underground is where you get all these flavor complexities, all the microbial activity,” says Bill Easton, of Terre Rouge and Easton Wines in Amador County. Because of these deep roots, “older vines are just greater translators of that complexity.”

Vague terms like “concentrated” and “intense” get thrown around a lot, sometimes attributed to old vines’ low yields. Like an older person, the analogy holds, an old vine speaks less, but chooses its words more wisely. On one hand, that may be a function of the yield balance that Passalacqua mentions; on the other hand, these lower yields may be a sign of general decay. “I work with a vineyard planted in the 1880s,” says Daniel Roberts, a vineyard consultant based in Sonoma County. “And the vines are as dead as they are alive.

Is it worth keeping them on life support? Is the fruit delicious enough to justify what may be an economically untenable situation?

Some say no.