I was caused to think about minerality and its causes once again by the conjunction of two events: I was impressed by the classic minerality of an old Burgundy; and I saw an interesting explanation of the phenomenon in pages from Filip Verheyden’s forthcoming book, WINE.

What is minerality anyway? A bit like pornography, you know it when you see it, but it is hard to describe where to draw the line. Personally I view it as a sort of flinty, smoky, precision, sometimes associated with a clear touch of gunflint, always with good acidity. It’s a classic feature of traditional Chablis and some other white Burgundies; perhaps it is clearer in Chardonnay than other white varieties because it stands out against the full body and opulence.

The wine that prompted me to think again about the issue was Domaine Leflaive’s premier cru from Puligny Montrachet, Les Clavoillons, when I just drank my last bottle of the 1996 vintage. It showed Leflaive’s hallmark style of a steely backbone, a whiff of gunflint (there’s that minerality), and a great sense of precision to the fruits on the palate. While there are some other Puligny’s in this style, Leflaive for me is its epitome. While the wine has all the richness you expect from a Puligny premier cru, it conveys to my mind a definite sense of minerality. I have drunk my way through a case of it, starting a couple of years after the vintage, and it has matured steadily from an initial sense of opulence to showing more clearly its steely structure as the baby fat of the young fruits slowly resolved. For me it’s shown a full blown mineral style roughly since 2004.

Surprisingly little is known about the causes of minerality. The one thing we can be sure of is that it does not come from taking up minerals from the soil. Minerals are present in trace amounts in grapes, and therefore in wine, of course, but far below the threshold at which they could influence taste: in fact, if minerals accumulated to the point at which you could sense them directly, it would probably be illegal to sell the wine. The only compound that’s ever been associated with minerality is a thiol (sulfur-containing compound), benzenemethanethiol, which might be a component of smokiness. This leads to the thought that minerality might basically be a consequence of the presence of reduced sulfur compounds in wine. But why should this be a feature of wines from specific places?

In his new book, an introduction to wine that succeeds in presenting major issues without pandering to simplification or the purple prose so beloved of some wine writers, and which is beautifully illustrated (and I recommend the book for mavens as well as novices for its prose and insights), Filip suggests that minerality develops in wines coming from grapes that are grown on poor, stony soil. The critical feature is not so much the presence of the stones as the fact that stony soil is poor in nutrients. The lack of nitrogen forces the yeast to utilize sulfur-containing amino acids as an energy source during fermentation, and in so doing, they generate volatile thiols that give the wine its impression of minerality.

This idea gives a practical explanation for a suspicion I’ve had for years about the connection between thiols and minerality, but I still find several aspects confusing about the connection. If minerality is related to the presence of thiols, it should be less evident in wines that have had more oxidative treatment, because oxygen destroys thiols. You might think this would mean that Chablis matured in stainless steel would be more prone to minerality than Chablis matured in oak (because there is more oxidative exposure in oak barrels), but I’ve never quite been able to convince myself that there’s a correlation. And if the connection is true, shouldn’t minerality decline as a wine gets older and has more exposure to oxygen; but the impression of minerality in my Clavoillons definitely increased after the first few years.

And that brings me to the problem that plagues white Burgundy today: premature oxidation. For more than the past decade, white Burgundy has erratically taken a sudden dive into oxidation. Premier or grand crus that used to last ten or fifteen years – indeed that might not even peak until after a decade – suddenly begin to decline after four or five years, showing notes of madeirization. No one knows the cause: some suggestions have been quite hilarious, such as changes in mowing between the rows, others have a ring of plausibility, such as increased battonage (stirring the lees when the wine is in the barrel, which tends to increase oxidative exposure), use of lower sulfur levels at bottling (sulfur protects against oxidation), and so on. The most obvious explanation lies with the corks: Philippe Drouhin told me that it is typical to find a case in which some bottles may be oxidized while others are perfect. “What could be the difference between them, except the cork,” he asks. (I wondered for a while whether the problem reflected changes made when corks stops being washed with chlorine, but if the solution was that simple, it would have been found by now.) The puzzle for me is why premature oxidation should affect white Burgundy so widely. Whether it’s practices in viticulture or vinification, or a deficiency in the corks, why should it seemingly affect all producers; they don’t all have identical practices or the same suppliers of corks.

So that brings me back to minerality. Reduction and oxidation are yin and yang. If minerality is indeed due to thiols, it requires (relatively) reduced conditions; having more reduction, should mineral wines be less prone to premature oxidation? Actually, it is my general impression that white Burgundy in lusher styles is more prone to premox (as it is abbreviated in the trade), but I can’t really support that assertion systematically. Could a difference along these lines explain why Chablis seems to suffer from it less than the Côte d’Or? On the other hand, the only time I have had a prematurely oxidized Chablis, it was from a producer famous for his use of stainless steel rather than oak. Every time I think I’ve found a correlation that might reflect a basic cause, I’m confounded by a counter example. It’s very confusing. In the meantime, I’m forced to drink my white Burgundies up to a decade earlier than I used to, which is very annoying.

The most amazing thing of all is that in spite of great advances in placing viticulture and vinification on a more scientific basis, we still don’t really understand in detail the effects of oxygen. That it has a dramatic effect is clear: anyone who has tasted the same wine bottled under both corks and screwcaps knows that after even a few months, you have two different wines. This has to be due to differences in oxygen exposure. There isn’t any agreement on whether oxygen is needed for the aging of red wines (by breathing through the cork), and the pros and cons of corks and screwcaps continue to be debated partly because of this lack of understanding. But that’s a topic for another day.

Tasting note

Domaine Leflaive, Puligny Montrachet Les Clavoillons, 1996

I hate to say it, but they just don’t make Burgundy like this any more. The nose is pure gun smoke and flint, very Puligny, very Leflaive. Complex palate mingles peaches and cream with citrus, the latter showing especially on a long textured finish, with a lovely balance. The palate has broadened out with age and has reached the heights of elegance and is sheer perfection after fifteen years. A grand cru might have a little more weight, but it could not have a better balance and flavor spectrum.