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The Ghost in the Wine

By: Jeff Cox

We read a lot about minerality in wine—the taste and aroma of minerals, flint, chalk, gravel, slate, stones, and such–but what is that, exactly?

Is it minerals mined from deep in the soil by a grapevine’s roots? Does it develop as grape juice turns to wine? Is it a specific compound or compounds that can be scientifically identified? Or is it something ineffable, more art than science, a ghost in the wine that can’t be explained but whose presence is subtly perceived?

Wine writers and critics seem very familiar with it. I can remember expressing my enthusiasm for a recent vintage of winemaker Richard Arrowood’s ‘Reserve Speciale’ Chardonnay from Sonoma County because of its huge core of minerality. But I realized, too, that I literally didn’t know what I was talking about.

Neither does Arrowood. “I don’t use ‘minerality’ in describing my wines,” he says. But he’s aware of it. “Minerality to me is like when you put stones in your mouth as a kid—there’s a subtle taste there…It’s a combination of clean earth and rock. You find it in Chablis and Meursault, but it’s not scientific. I have no idea where it comes from.”

Since it’s such a common term, I thought The Oxford Companion to Wine might have an entry on minerality. But no. It lists the minerals found in wine—sulfur, magnesium, potassium, calcium, manganese, iron, copper, zinc—but makes no mention of them in relation to the stony quality of minerality. Similarly, the Wine Aroma Wheel invented by Dr. Ann Noble at UC Davis makes no mention of this quality.

Maybe wine scientists have nailed it down. I called Dr. Hildegarde Heymann, Professor of Enology at the University of California, Davis, who specializes in the descriptive analysis of wine. She has some ideas: “I think minerality might come from a complex of sulfur compounds found naturally in the grapes—not the sulfites added as a preservative. But I have no scientific basis for saying this,” she said.

Dr. Heymann says she would like to research the nature of minerality, but that no one has stepped forward with money to fund the studies—yet. Because it exists in the realm of jargon rather than science, she says, “It’s not a word I use.” Despite the disclaimer, she describes how bottle age may affect minerality: “It seems that wine can lose some minerality over time. Sulfite compounds are very reactive in wines as they age,” she said, and as they react with other compounds in the wine, their contribution to minerality may lessen. She finished our discussion by repeating, “I have no scientific basis for saying this. Minerality is not a word I use.”

Mick Schroeter, winemaker at Geyser Peak Winery in Sonoma County, also begs off the word. “Minerality is not a term we use at Geyser Peak that often,” he says. “When we do use it, it’s usually a descriptor for Sauvignon Blanc. It would also be applicable to Pinot Gris and white Burgundies. I see it as a character on the nose or palate likened to the smell of wet stones, wet gravel, or wet pavement. It may also be likened to the soils the grapes are grown in and the impact those soils have on the character of the wine; for instance, the calcareous soils in Burgundy.”

“Minerality is a perception people have, but it may not be specific compounds that produce it,” says Dr. Susan Ebeler, Professor of Viticulture and Enology at UC Davis who specializes in wine analysis and sensory chemistry. “That is, people might not be talking about the same thing when they say minerality. Is it in the alcohol? In the salts? There’s no clear answer. Maybe it’s simply subjective. For it to be objective, we need a reference standard so that people can always say, ‘That’s minerality!” when they encounter it. But we’re not there yet.”

The French seem to know what it is, and for many of them, it’s at the core of their cherished concept of terroir.

“Minerality is the essence of terroir,” says Olivier Portet, Director of European Imports for Wilson Daniels, the Napa Valley-based wine sales and marketing company. This firm carries a portfolio both domestic and imported that is stuffed with wines showing what Robert Parker calls “liquid minerals.”

“Minerality is more the core and essence of a wine than the fruit components,” Portet said. “The Loire Valley, Burgundy, Alsace, and Chablis all show this quality. You can see the reflection of white chalk soils in the wines of Blagny (in the Cote d’Or). Minerality is strong in white wines in France. In fact, more infertile soils show more terroir.” While minerality is found in red wines, the stronger phenolics, tannins, and other robust components of red wines tend to cover it up.

Maison Louis Jadot is one of Burgundy’s premier negotiants. Jadot’s Cellarmaster Jacques Lardiere says flatly, “All our wines carry minerality.” He says the acidic cell contents of the microorganisms in the soil dissolve minerals from the bedrock, and the grapevines then absorb these minerals.” This minerality applies to both Chardonnays and Pinot Noirs because their fruit depends on the same bedrock. The minerals in Burgundian soils create coherence in the wines, from the least to the greatest cuvees. But there exist places that are able to reveal this mineralization with more dynamism.”

In other words, the taste of Burgundy can be found in its wines and the greater the cuvee, the more it tastes like Burgundy. That may be so, but is the minerality that can be found in wines from around the world really due to the uptake of soil minerals by the vines? Terroir shouldn’t be conflated with minerality. The former is a quality in the wine that defines a particular place. Minerality is a quality in wine that cuts across boundaries and is present not only in Burgundy, but in most wine growing regions of the world.

We’re back to square one. What then is minerality?

Portet hit on what may be the answer to our question when he said, “…more infertile soils show more terroir.” And they may show more minerality. At least, that’s the theory of winemaker and wine educator John Buechsenstein. He unraveled his compelling theory of minerality and what it actually is during an interview.

“Minerality is a new buzzword in wine, so it would be great to come to a common meaning for it,” he said. “I think I know what it isn’t. It isn’t old vines reaching deep in the earth and bringing up bits of earth and rocks. Those deep roots are after water. Most nutrients, including minerals, are taken up by feeder roots in the top layer of soil.

“For a long time I’ve thought that maybe the source is environmental. That is, low level moldiness or earthiness picked up in the winery. I’m thinking about the ancient wine cellars in Germany,” he said. I flashed back to similarly ancient and somewhat moldy cellars I’ve seen in France.

“But then,” he said, “how do you explain minerality in wines from brand new wineries? I thought maybe it was moldy barrel staves that might be the source of minerality, but I don’t know. I’ve discarded the environmental source idea, but it’s still always in the back of my mind.

“It also might be caused by a reaction between strong acidity in a wine and compounds known as pyrazines,” he said. Human beings can detect pyrazines in vanishingly small amounts, such as parts per trillion. “One drop in the Reflecting Pool in Washington, DC, and you’d smell bell peppers all the way to the Beltway.” Put another way, “If you could extract all the pyrazines from 60 million liters of Sauvignon Blanc, it would hardly fill a thimble. Minerality could be really low levels of pyrazines.” He pointed out that “grassiness” in Sauvignon Blancs is caused by pyrazines.

Then Buechsenstein revealed an explanation that made real sense to me.

He said that another candidate source for minerality in wine is mercaptans. Mercaptans, also called thiols, are molecules containing hydrogen and sulfur—hydrogen sulfide (H2S), for instance, is not uncommon in wine. When it’s present in large enough amounts, it smells like rotten eggs. But in very small amounts? Here’s what Buechsenstein had to say:

“Wines with minerality often come from Old World, cool climate sites that have been farmed for centuries, even thousands of years. Their soils are thin and rocky—worn out from so many harvests. What creates sulfides (mercaptans) in wines? Musts that are poor in nitrogen. Yeast needs a certain amount of nitrogen to grow. If a must is nitrogen poor, then the yeast will start cannibalizing amino acids they find in the must. There are two amino acids that have sulfur in their molecules—methionine and cysteine.

“At the core of amino acids is a nitrogen group. So the yeast goes after the nitrogen in the aminos. They use the nitrogen to survive, but when methionine and cysteine are deconstructed, the sulfur is released into the must, which then goes through a reduction process to form mercaptans

“That’s why,” he said, “winemakers treat a stinky must with yeast assimilable nitrogen, such as diammonium phosphate. The yeast are given enough nitrogen to stop attacking the amino acids and liberating the sulfur.

“You know, in the old days in Europe, grapes and olives were planted where you couldn’t grow anything else, such as up on the rocky hillsides. These sites are naturally low in nitrogen, and that may be the cause of nitrogen scavenging by yeasts and the production of low amounts of mercaptans.

“So,” he said, and I could see the educator in him rising to the conclusion, “minerality could be trace amounts of mercaptans in the wine.”

I’ve smelled enough hydrogen sulfide in wine to know that it is a really unpleasant offense to the nose. That in very tiny amounts it might actually be the cause of minerality—a very pleasant sensation in wine–is an interesting thought. But, I wondered, why would human beings have evolved an olfactory sense so heightened to mercaptans that it can detect parts per trillion in a glass of wine? What’s the evolutionary value in that?

So I contacted Dr. David Rand, Professor of Biology at the Department of Ecology and Evolutionary Biology at Brown University and asked him. He responded: “I think the simple answer is that there is an evolutionary advantage to being able to detect vanishingly small amounts of any odors, and mercaptans happen to be one of them…Interestingly, humans have many more…odor receptor genes than chimps. The connection to wine is a red herring. Rather focus on the importance of detecting anything good or bad in the things ancient humans wanted to eat or mate with.”

Perhaps it’s true—many things that are bad for us in quantity are good for us in very tiny amounts. That’s the basis of homeopathy. It might also be the basis for the fine minerality that so pleases our palates.

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    Theresa Dillon

    Theresa Dillon
    Theresa Dillon earned her bachelor’s degree in print journalism from the Walter Cronkite School of Journalism and Mass Communication at ASU. In her spare time she enjoys reading, attending concerts, weekly trivia nights, watching movies (especially her favorite The Wizard of Oz), and of course wine.