In the latest of his deep dives into wine’s most significant soil categories, Alex Maltman explores the properties of flint, and attempts to understand how this inert substance became such a popular wine-tasting descriptor.
All of us have heard of flint. To some it means prehistoric tools; to some it’s the gizmo that makes sparks in cigarette lighters; and to some farmers it’s the damnably hard field stone that wrecks machinery.
But for most readers of this magazine, the word almost certainly conjures up certain kinds of wine—Chablis or Sancerre, perhaps. “A quintessential Sauvignon Blanc with the telltale hint of flint”—that kind of thing. In fact, words like flint and flinty are these days among the most commonly seen terms in wine descriptions.
It seems people like the word. You can buy a “flint” guitar and “flint” shoes (oddly enough from a shop called Margaux). You can buy “flint” coconut bars and “flint” bread snacks (caviar-flavored, no less). It crops up in popular culture—Van Morrison’s voice has been likened to flint—and it’s a much-used word in literature. Ebenezer Scrooge’s heart was “hard and sharp as flint.”
Shakespeare liked to mention the names of rocks and minerals in his plays, but the one he used most often was flint. It’s versatile stuff, too. Should you be worried about your eyebrows: “our loose mineral flint will help fill in sparse brows while looking absolutely natural.”
This multitude of allusions presumably stems from the material flint itself and the way we perceive what it is, how it behaves. So, what exactly is this potent, charismatic substance?
Flint is made of silica—that is, silicon dioxide. The two elements silicon and oxygen are bonded together in an ordered three-dimensional framework—what in science is called a crystalline arrangement—but each crystal in the flint mass is truly tiny. It’s no more than a 20,000th of a millimeter across, about the thickness of plastic clingwrap.
Geologically, it’s this extreme fineness that distinguishes flint from silica minerals such as quartz and amethyst, with their sizable crystals.
All silica substances, irrespective of how large the individual crystals are, have this efficient three-dimensional packing of the constituent silicon and oxygen, and this has crucial repercussions. For starters, there are no planes of weakness within the meshwork, so the material breaks in a special way.
Besides the enormous practicalities of this in prehistory, I shall explain later how this might just impinge on our using flint in wine-tasting notes. It makes the material hard and tough, as implied in the literary allusions mentioned above, and this has practical implications for vineyards. It also makes flint chemically inert and virtually insoluble, which, among other things, means it is odorless and tasteless.
Hmm. This raises tricky questions about what we actually mean by saying a wine smells or tastes “flinty.” I will be returning to this intriguing issue.
How does flint come about in nature? Essentially, it forms from the decayed silica skeletons of tiny creatures that inhabit the world’s oceans. Favorable conditions for this have arisen a number of times in Earth’s history, including the present day, but they hit an optimum around 90 million years ago, during a geological period called the Cretaceous.
The climate then was exceptionally warm, sea levels were high, and considerable parts of the Earth’s surface were covered by sunlit shallow seas, rather like the Bahamas today. Calcareous creatures such as corals abounded and produced sea-floor sediment that would go on to make limestone.
And at this particular time in the Cretaceous, the dominant oceanic organism was a calcareous plankton whose remains (called coccoliths) gave rise to the particular kind of limestone we call chalk.
From time to time, however, there were also huge numbers of little creatures made of silica, such as diatoms (tiny cells of algae said to be floating in the oceans today in such numbers they account for a quarter of all the photosynthesis on Earth) and the beautiful glass-like architectural marvels called radiolaria.
When these organisms died, their silica skeletons accumulated on the sea bottom and, with time, turned into a gelatinous mass. Then, upon becoming buried a few meters or so, the material became sufficiently reorganized internally to make the finely crystalline matter we know as flint, forming bands and lumps within the calcareous sediment that was to become limestone.
So, the chalk that formed during the Cretaceous period—now uplifted and, in places, making cliffs and crags for us to see—may well contain flint. Important for vineyards, however, is the detritus formed by the weathering of these rocks. The toughness of the flint preserves it as pebbles, to be redistributed by rivers as gravel. And typically, this is how we see it in vineyards: spread out across the ground.
Where in the world?
Flint is not an abundant mineral, but it’s widely distributed. It pops up in places from southern Scandinavia, to the coast of South Australia (where, I read, one grower crushes the flint stones in his vineyard into smaller pieces, believing that this leads to greater flintiness in his wines).
Curiously, pieces of flint are also found in Australia around Sydney Harbour—“curious” because there is no natural flint anywhere nearby. So, where did the pieces come from? The most likely answer is London. It seems that when convict transport ships were being outfitted ready for the long voyage to the colony, stones—including flint—were taken from the banks of the River Thames to serve as ballast and then dumped on arrival in Sydney.
In North America, flint is widespread and of various geological ages—it occurs, for example, in Maine, New York, Missouri, and Texas. Flint is the official state gemstone of Ohio. Artifacts made from it, dug from Flint Ridge in eastern Licking and western Muskingum counties, have been found right across the present-day eastern United States and as far west as the Rocky Mountains.
But of those warm Cretaceous seas I mentioned earlier, the most extensive development was the huge, albeit shallow, ocean that spread from what is now the British Isles, across northern and central Europe, to the Middle East, Crimea, and Kazakhstan.
And that is why, incidentally, limestone happens to underlie so many of the classic wine regions of western Europe. (It’s fascinating to speculate on how vineyard geology might be viewed if geological chance had produced some other kind of rock in, say, Burgundy.)
Of course, the limestone produced in that big Cretaceous ocean isn’t seen everywhere at the present-day land surface, and the flinty parts certainly aren’t. But it seems that the conditions for flint formation reached their apogee in and around what is now eastern and southern England and north-central France.
It was here that prehistoric man found the best flint for making tools, with perhaps the most desirable material of all coming from around Grimes Graves in Norfolk, England, and Le Grand Pressigny in the Indre-et Loire region of central France; more on these two remarkable places later…
In line with the above, parts of East Anglia (tipped for future vineyard expansion) have very flinty ground. Already well established there is Norfolk’s Flint Vineyard, with its eponymous soils.
Vineyards on England’s South and North Downs, together with those in mid-Dorset up through Wiltshire and northern Hampshire are flinty—examples are Tinwood, Westwell, and Langham Wine Estates, and Danebury vineyard. Wiston and Highdown vineyards on the South Downs are only a few miles away from the prehistoric Cissbury flint workings.
In France, parts of the Champagne area, such as the Côte des Blancs and the Côte de Sézanne, are famously flinty. So are parts of the Loire Valley, such as at Vouvray.
But probably the most quoted instances are at Pouilly and Sancerre, home of the often-claimed connection between the soils and a flinty aspect to the wines. But besides the scientific difficulties with that, it’s noticeable that most of the sites there aren’t particularly flinty.
In Sancerre, flint soils occur at St-Satur, Ménétréol, Thauvenay, and at the top of the hill of Sancerre town itself; in Pouilly, St-Andelain is the best known site for flint, together with Tracy, where some vines are actually planted in an old flint quarry. Even so, other kinds of soils account for fully 80 percent of Pouilly and Sancerre.
Flint-bearing rocks are found sporadically across Eastern Europe and the Middle East, in some cases coinciding with wine-producing areas. In Bulgaria, for instance, flints occur in both the Thracian Lowlands and Danubian Plain wine regions, and in the Marmara wine region of Turkey’s Thrace Peninsula. Kefraya, to wine enthusiasts, is the name of the winery in Lebanon’s Beqaa Valley, born in wartime but surviving to produce what is arguably the country’s benchmark wine.
But to archaeologists, it’s the term for the special kind of flints found there. Unusually large Neolithic flint workings extend about one mile (2km) northwest of the Chateau Kefraya winery.
Returning to France, away from the Champagne/Loire swath of flinty bedrock, the notable occurrences of flint are as loose debris, typically in spreads of river gravel. For example, deposits of flint pebbles come and go along the left bank of the Garonne and Gironde, having been eroded from the Pyrenees and transported northward.
You can see them in parts of Graves, say around Martillac, on some of the gravel rises in Margaux, and in Begadan in the northernmost Médoc. Some of the beaux cailloux at St-Julien’s Château Ducru-Beaucaillou are flint.
Finally, a sign that you’re in flint country, more obvious than looking for vineyard pebbles, can be the local building material. The odd shapes of flint lumps make them an awkward masonry stone, costly and time consuming to work, and hence they were often only used for churches and other buildings of status.
How they were worked changed through time. In East Anglia, early buildings were of coarse and unsplit flint alone, but at a later time it was combined with other materials, in fancy bands or checkerboard patterns.
Then it became fashionable to trim the flints to square surfaces so they could be framed—so-called flushwork. The various patterns have names like “concentric,” “bird’s beak,” and “snail creep.” It’s a whole different world of flint!
Flint in vineyards
You can bet that most growers who have flinty vineyard soils are going to use that in their marketing, in just the same way as other producers trumpet their particular geology. It seems to me, however, that in reality, having flinty soils is something of a mixed blessing.
First, the advantages. It sounds good and lends itself to promotional prose. And in particular, the popular idea that flinty soils imbue wine with a special flintiness is an effective and frequently used selling point.
Maybe they do, but it would have to be in some complex, indirect way. Vine roots are demonstrably incapable of absorbing and using a solid, inert compound such as silica, which is tasteless anyway.
This isn’t to dispute that flinty wines are produced from flinty soils; the issue is to what extent it’s the soil that’s responsible. Clearly, numerous producers with flint are convinced it’s the key; but on the other hand, plenty of flinty wines are produced on soils without flint—Chablis is an obvious example—and vice versa.
The other advantage frequently claimed for flint pebbles is their absorbing heat during the day and re-radiating the warmth at night. But again, growers with other kinds of rocks make the same claim, and it’s of doubtful benefit anyway.
The scientific data show that this thermal behavior varies little between differing rock types—all rocks do it (provided the ground is bare)—and that it’s not a very great effect in practice. It’s probably only significant in some cool-climate areas where the grapes are trained close to the ground. And there is also a school of thought that finer grapes are produced where nighttime temperatures are markedly cooler than during the day.
Flint pebbles provide good drainage, and being inert, they restrict nutrient availability, giving meager soils that tend to deliver finer grapes. At the same time, in overly dry areas, the pebbles can promote the localized formation of dew, which leads to increased microbial activity and more organic matter beneath the stones. All this promotes a good soil structure, though it’s the existence of the pebbles that does the job, not that they’re made of flint.
The disadvantages arise from the practicalities of working the vineyard. I’ll discuss shortly how flint can have sharp edges, and in the vineyard this can lead to punctures.
In addition, flint pebbles are hard and tough enough to damage farm machinery—there are plenty of stories of broken harrows, twisted mower blades, and dented cultivators, all of which cost time and money.
Moreover, when the steel of an appliance strikes a flint pebble, there may well be a spark, and in dry conditions a fire could be started. Just last year, the Harrow & Hope vineyard in Buckinghamshire suffered fire damage from sparks that took hold in dry grass. At Domaine de la Chezatte in Sancerre, water buckets are scattered throughout the vineyard ground in case machinery sparks a fire.
So, although flint has a certain allure, it has practical snags; there are pros and cons. Rathfinny vineyard in Sussex, England, tackled the dilemma by removing flint chunks from the vineyard—more than 112 tons of them—and then highlighting the flint in the construction of new winery buildings.
So, now their B&B guests, rather than pondering in the vineyard on the value or otherwise of the stones, can delight in the charisma of flint in the walls of their accommodation.
Flint in wine
Now we come to the heart of the matter: flint in your wine. Some of the most frequently used words in today’s wine descriptions are “flint,” “flinty,” “gunflint,” and the like. And no doubt all wine lovers will know precisely what the terms mean to them.
Trying to explain the meaning to others, however, begins to reveal some formlessness to the words. Describing a wine as showing a “whiff of gunflint” seems precise and unambiguous, but as we shall soon see, on examination it isn’t so.
An immediate difficulty is the inertness of silica, such that geological flint is without taste or smell. That’s why diatomite—made of silica—is widely used in wine filters: It doesn’t taint. It’s why silica is used for wine glasses and bottles; in trade-speak, the clear bottles used for white Bordeaux wine and some spirits are known as “flint glass.”
So, when we use flint to communicate a taste perception, it can’t be literal; there has to be something more metaphorical going on.
Flint is most often used in describing acidic, perhaps cool-climate, white wines, though it isn’t restricted to them. For example, “Cayuse Grenache has an abundance of concentrated dark fruit and an unmistakable flinty streak”; “Chave Hermitage has a flinty, velvet texture, and almost weightless concentration”; “Priorat is known for bold and always flinty wines.”
These are all referring to red wines, and rich ones at that. For some, sweet wines can have it, too: the “Château Guiraud was very mineralic, fresh, and flinty”; Château La Tour Blanche Sauternes offered a “flinty, citrusy, buttery nose”; “the wines of Barsac tend to be almost flinty.”
For that matter, Glen Grant whisky is “very flinty,” and Ardbeg 12 Year Old has a “flinty finish,” while “the volcanic soils of Aveyron, France, create flinty cheeses.”
There is a plethora of pronouncements out there on what flint means in describing wines—and debate on whether it is an aroma, taste, texture, mouthfeel, or some combination.
I suggest that three aspects of flint, the geological substance, are at the root of things, and I will look at each in turn. But first let me make it clear (parallels with minerality here?) that none of the following is to suggest that using these flinty words is wrong or that we should abandon them.
They may on scrutiny lack precision, but in the difficult business of putting perceptions into words they’re clearly very useful devices.
Flint has the edge
What do the following have in common? The Les Chailloux (Sancerre) is “wonderfully chiseled and flinty”; 2016 Le Craie, Vouvray, shows “a flint edge that seems angular”; the 2015 Chablis Vaillons “has a touch of flint-lending edginess.”
It seems to me that they’re all alluding to the physicality of geological flint and its well-known propensity to break with angular edges.
We’ve all seen pictures of prehistoric flint tools and perhaps admired their exquisite craftmanship. But here’s an extraordinary thing: For ages, flint was absolutely central to the livelihoods of our ancestors. They—or, seeing as they’re our forebears and we’re all the same species, we—knew exactly where to get flint and how to fashion it into the tools that were so essential. We did it for over 99 percent of our history.
Then suddenly, in Europe at least, we simply forgot all about it. It vanished from memory. So, when in medieval times people started noticing flint arrowheads on the ground, we were at a loss as to what they could be.
Most ideas involved them having fallen from the skies, and in those religious times a common belief was that they were debris from celestial battles involving Satan. It wasn’t until travelers returned from abroad, having seen flint still in use, that we rediscovered the real nature of these objects.
That was far from the end of it, though, as more troubling questions then emerged. In places these man-made tools were found buried beneath several meters of sediment that had accumulated through time, alongside the bones of mysterious creatures such as mammoths and the European rhinoceros.
How could this be? Mankind was a creation separate from nature and had been placed on Earth only recently—few at the time questioned that.
The arguments that followed were impassioned and prolonged. Scientists had to be particularly cautious with such sensitive things, especially in a field beset by fraudsters—remember the Piltdown epic? Even by the time of On the Origin of Species, Darwin felt it safer just to sidestep saying how man fitted in.
And here’s another, I think, intriguing thing. Archaeologists used to think that this ability to craft tools was the defining feature of modern man, Homo sapiens, so it could only have been done during the past 2,000 years or so at the most.
Now, not only have manufactured tools been found dating back well over 3 million years and produced by several different species of our hominid predecessors, but they have also been observed being made, albeit crudely, by chimpanzees and bonobos.
All of this comes about because of the particular way in which flint breaks. It’s that three-dimensional meshwork again. A fracture curves as it spreads through a solid unless there are guiding weaknesses, which is the case with most materials.
Silica, however, with its efficient internal framework, has no such weaknesses. Consequently, all silica materials, including flint, quartz, and glass, break in this curving way. Two curves meeting each other produce an edge, and three or more give a point.
The curves are what geologists call conchoidal fractures. Sounds like new-fangled jargon? Conchoidal was being used by the mathematician Nicomedes in around 200 bc, when he likened the form made by lines dividing certain angles to the shape of a conch shell.
The term fell into disuse but was resuscitated by mathematicians in the 18th century—which was just the time that geologists were systematically describing the properties of rocks and minerals, and they coopted the word.
I’m not suggesting that a flintiness in wine simply indicates sharpness or acidity, but perhaps, subliminally at least, this edginess is part of the context. Incidentally, that figure who is something of a modern messiah to some in the wine world, Rudolf Steiner, pronounced specifically on how silica breaks.
Most of his proclamations are mystical and untestable, but during a talk on the ego and meditation, he stated, “Take a quartz crystal. If you take a hammer and break it up, the single pieces retain the tendency to be six-sided prisms, capped by six-sided pyramids.”
(He went on to assert that from the pieces “something living and cosmic” emerges.) But manifestly, quartz crystals don’t break like that; it’s easy to demonstrate that they break into curving, shapeless fragments, just as with glass.
Most instances of flint in tasting seem to be referring to its aroma. Because geological flint has no smell, however, this cannot be literal: Geological manuals list more than a dozen technical properties of flint (color, hardness, translucency, and so on), but none of them mentions smell.
So, more than likely the references are to the distinctive odor of two lumps of flint being rubbed together. Indeed, I read in a popular UK wine magazine that “if you want to experience what flint smells like, next time you are walking in the South Downs, pick up two pieces of chalk and rub them together.”
Wrong material (chalk is a very different thing from flint) but right idea.
Scientists now have a grasp of how the smell of abrading flints comes about, thanks to their selfless quest for a better understanding of the world around us. A Swiss team was studying toilet malodors—yes, toilet malodors—when they accidentally isolated “a ﬂint-like odor, similar to the smell associated with a dentist drilling teeth.”
They were able to show that it was due to one compound in particular: hydrogen disulfane, or HSSH. Natural flint always contains impurities (which is why its colors are so varied), among them sulfur. And it turns out that from this and the energy input from rubbing the flints together in air, tiny amounts of HSSH gas are generated from the flint surface.
But here’s the thing. A panel of wine professionals tasted various Swiss Chasselas wines and judged that two of them were far more flinty than the others—and those two contained significantly more HSSH than the others.
So, if we call a wine flinty, it may well contain HSSH, and subconsciously or otherwise, we might be recalling the odor of striking flint pebbles against one another. It’s a mental association.
It makes sense to me, except I’m not sure how many tasters happily describing a flinty note in a wine will actually have banged two pieces of flint together. I suspect that, as with a number of other wine descriptors, we imagine what the smell should be like.
Other studies have related flinty aromas in wine with the presence of another sulfur compound, benzenemethanethiol. Apparently, we can detect this in astonishingly tiny amounts—as low as 0.3 parts per trillion—and levels of over 10 parts per trillion have been measured in some Loire Sauvignon Blancs.
The rubbing of flints can hardly be happening in a grapevine, of course, and these sulfur-bearing compounds aren’t present in grapes. They’re generated during the vinification, especially during the yeast fermentation.
It’s a further illustration that although we may be labeling our perception as flint, there’s no direct connection with any flint that happens to be in the vineyard.
No doubt some winemakers seeking to increase flintiness in their wines will be tempted to nurture these sulfur-bearing (reductive) compounds. For instance, they could eliminate stirring of the lees and minimize racking—or go online and, for a mere £142, buy a 250mg bottle of benzenemethanethiol…
The great gunflint saga
A third variation on sensing flint in wine, besides sharpness and the aroma of abrading flint, is that of referring to “gunflint.” So, we’re now in the realms of flint and fire, sparks and smoke.
And famous is the association of flint with sparks and making fire, though there are an awful lot of hazy (or should that be smoky?) misconceptions about it.
Let’s be clear: Bashing two pieces of flint together will not make a spark; flint cannot spark. Flint doesn’t “contain fire,” as one poet had it. It all comes back once again to that inertness of silica: Flint cannot vaporize (and so, as we have seen, lacks odor), and therefore it cannot ignite.
So, where do those legendary sparks come from, if not from flint? The story is fascinating.
Early man exploited fire. For a very long time this involved manipulating natural fires to our advantage, until at some relatively recent time we learned how to create fire. At first, we used the frictional heat from rubbing woods together, and then by striking the mineral pyrite (iron sulfide) on a harder material such as flint, which sometimes makes a spark.
Everything changed when we learned how to manufacture metals. Discovering bronze signaled the end of the Stone Age and our dependence on flint tools; and then making iron (which invariably contained impurities such as carbon, so in practice it was steel) finally gave us an effective and reliable way of making sparks and hence creating fire.
We soon learned that striking steel on something harder—and flint was familiar and ideal—almost invariably gave sparks. Then, with some dry tinder we could create fire. But it is the steel that sparks, not the flint. The smell is burning steel.
It is true that striking pieces of flint together in a darkened room may give a visible pulse of light. But this is the curious phenomenon of triboluminescence, in which the energy of breaking chemical bonds is converted into light.
That sounds very technical, but the effect is easily seen with familiar materials—try yanking apart two pieces of adhesive tape or crushing a sugar cube. The point is that this doesn’t produce heat, nothing burns—there is no smell.
Certain substances in the presence of oxygen are capable of spontaneously bursting into flames—that is, they are pyrophoric. Sodium, potassium, and calcium, for example, are extremely pyrophoric. It’s why, if you can recall these elements in your school chemistry lab, they would have been kept under a liquid, to exclude oxygen and avoid spontaneous combustion.
The phosphorus used in match heads needs the addition of a little heat, such as from the friction of striking a match. The mineral pyrite and a few metals—and iron is one—can be struck such that the surface area of any tiny particle that breaks off becomes exposed to sufficient oxygen for it to auto-ignite, thus making a spark. And that tiny speck of burning iron makes the distinct burning smell.
It’s easy to get steel to do this by striking it on some hard, tough material—like flint. And if you’ve ever done it, it might be useful to remember that smell when trying to describe a wine. But clearly, in wine tasting, it must again be an allusion, a mental association. Vines and wines don’t involve bashing and combustion.
Historically, things entered an ominous new era when gunpowder appeared in Europe. When ignited by a spark, this amazing powder burned so rapidly that if it was confined in a metal chamber, so much pressure was spontaneously generated that a projectile could be ejected at very high speed. We now had guns.
All sorts of ingenious devices appeared for striking steel on a flint and getting the spark to drop into the gun’s powder chamber. Then, around 1600, a spring-loaded mechanism internal to the gun was invented—the flintlock. It greatly streamlined things and became commonplace.
And as a result, flint mining suddenly underwent a staggering new lease of life. The great flint center of Le Grand Pressigny was resurrected, together with the extension of the Grimes Graves deposits at Brandon.
These two places, in France and England respectively, may not be well known, but they quietly underpinned a great deal of history. Their flints armed the pistols of the English Civil War and the French Revolution, the muskets of Waterloo and Crimea.
Patriots in the American War of Independence relied on French ammunition; in a way, the Revolutionary War was fought between flints from Pressigny and flints from Brandon.
So, I suppose the aroma of gunflint would have been familiar to the military folk of those times, together with hunters, felons, buccaneers, and the like. I can’t help wondering, however, especially seeing as modern firearms (together with barbecue, stove-top, and cigarette lighters) use synthetic rather than geological flint, how many of today’s wine commentators who blithely refer to a “gunflint” aroma have actually experienced it.
But in any case, there’s a bigger problem with this much-loved gunflint analogy. The overriding smell of a firing gun—antique or modern—is the reek of the burning powder. The odor of the spark within the confines of the gun chamber is lost in the smell of the exploding charge.
It’s one thing to strike a piece of steel on a lump of flint and smell the spark, but the odor of gunfire is different.
It seems to me that gunflint as a tasting term isn’t a direct comparison with firing guns but is a nice-sounding variation on the “smoky,” “struck-match” theme. Thus, tasting notes speak of “gunpowder-like smoky hints”; “as flinty as they come, with the smell of fireworks”; “intense aromas of gunflint and black rifle powder.”
And we may also be subconsciously involving a fair dose of imagination on what a gunflint ought to smell like. In turn, and extending this imprecision, this smokiness blurs into the rubbed-flint aroma of the previous section.
Whatever we mean by these various labels, there’s also the much-mentioned idea that they come from the soil. Things like “the flint in the soil gives the wine an aroma of gunflint.”
It sounds straightforward enough at first, but as I have indicated there are scientific difficulties with the notion. The claims never say how it works. Just how do obdurate, inert flint stones in the ground give “flintiness” to the finished wine?
From a scientific viewpoint, any connections between the soil and taste have to be complex and circuitous, and the “flinty” labels best regarded as metaphors—mental associations—conveniently describing flavors that largely arise during the winemaking.
I began by saying that we have all heard of flint. But I wonder how many appreciate how central the role of flint has been in the human journey. As we have glimpsed, flint has colored literature, influenced architecture, and underpinned warfare.
For 3 million years and more, human technology was dominated by this stuff, our livelihoods depended on it. You could even argue that flint is the single most important substance in all of human history.
Oh, and today it’s one of the most popular words for describing wine.