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A visiting Italian vintner recently handed me an unusual gift. I was about to respectfully decline the freebie when I noticed it was nothing more than a rock, about the size and shape of a Brazil nut. She had stuffed it into a cute little felt drawstring sack in a sort of flashback to the 1970s Pet Rock craze. But this nugget was truly special, she assured me. She'd plucked it from her most prized vineyard as tangible evidence of the source of her wines' celebrated "minerality."

"Grazie," I said, grateful for my new paperweight. But to me the rock was a blarney stone. There are no minerals in wine, at least not in concentrations perceptible by human beings or, for that matter, wine critics. Minerality – and I use the term myself – is a metaphor, a way to convey olfactory sensations associated with, say, the scent of wet stones or marble quarries or plaster dust or matches struck on flint. It's got nothing to do with minerals in the glass.

Yet it's increasingly being trotted out in a literal sense by winemakers and connoisseurs who believe they are tasting actual rock matter, most notably the famous limestone of Burgundy, the fossilized oyster shells of Chablis, Mosel's slate and Sancerre's flint.

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"The fruity, mineral style of the wine is a reflection of the three types of flint found in the vineyards," reads one recent product description by a Sancerre producer. "Strongly mineral nose – one might almost think it had been grown on the slate of the Mosel!" wrote British wine writer Jancis Robinson of an Australian riesling.

Flint, slate, wet stone, chalk, limestone, graphite – the list goes on. It's as though fine wine has become one big rock show.

"It is the buzzword," says Alex Maltman, a geologist and professor in the Institute of Geography and Earth Sciences at the University of Wales, Aberystwyth. "But before the year 2000, it didn't exist. It's come from nowhere and it's astonishing."

There's just one problem. All that rock talk doesn't hold water. At a gathering of the Geological Society of America in Portland, Ore., three years ago, scientists pronounced that the mineral content in wine is below the threshold of human taste and smell. There is more calcium and magnesium, for example, in S. Pellegrino mineral water than in a typical glass of chardonnay. In fact, if you add minerals in concentrations typically found in wine to distilled water, humans can't detect their presence.

"The actual concentration of these minerals in wine is minuscule, parts per million, typically," Maltman says. "In any case, these minerals have no flavour. They are tasteless, with the exception of salt."

Our olfactory systems are designed to detect vapours, and rocks are not volatile. While wet rocks do have a smell, that odour is produced by something other than the rock, most likely algae or other organic compounds that have pitched a tent on the surface.

If you want further proof of the absurdity of the discourse, consider flintiness, a common attribute ascribed to wines grown on rocky soils. "Flint is [a form of] silicon dioxide, or silica, and flint is tasteless," Maltman says. "Which is exactly why silica is used for glass. Wine bottles are made from silica. Wine glasses are made from silica. It's mined to make glass because it's tasteless."

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The idea that vine roots can probe directly into solid rock and transport minerals into grape juice holds strong romantic appeal. If you can literally taste the ground, the logic goes, the wine must somehow be pure, or at least relatively unmasked by large-scale industrial blending or the artifice of heavy-handed oak-barrel aging.

In that sense, minerality – taken literally – is the illegitimate offspring of terroir, a genuinely meaningful French term designed to capture how soil, weather and other environmental factors can yield flavour differences from one vineyard and another. Soil and weather do have a profound impact on a wine's taste – but they do so by promoting or curbing various aromatic organic compounds as well as by regulating acid and tannin levels. It's a scientific stretch, and a linguistic gaffe, to equate terroir with the presence of soil in your glass.

"That's not how plant physiology works," says Dr. Gavin Sacks, assistant professor of oenology in the department of food science at Cornell University. "The plant is very selective about what it will transport."

In other words, vines are picky eaters. Just because there's lots of calcium-rich limestone in the soil pantry doesn't mean plants will gorge on it. And key minerals such as calcium, potassium, magnesium, silicon and sodium mainly act as nutrients for the plant, modifying the balance of organic compounds that we actually can smell and taste.

So, what does produce those "minerally" nuances beloved by today's connoisseurs and critics? I have yet to encounter a scientist who knows for sure. But I think the best guess – and it's merely a guess – is a combination of acids or sulphur-bearing organic compounds produced by yeast during fermentation. How about that for a press-kit freebie? A drawstring sack full of yeast. Messy, but the truth often is.

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