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Before the world changed, I used to go walking on England's South Downs. The topsoil here can be so thin that if you scuff the grass with your foot you reveal white chalk. Chalk is brilliant for vines, isn't it? Yet if you plant vines on completely pure chalk, they will die.
Champagne is chalk, 300 meters thick; English growers often plant Champagne grapes on the same chalk where it rears up the other side of the English Channel. There is chalk in Texas: when growers needed wild American vines for rootstocks that would be compatible with the alkaline chalk soils of Champagne they found them here, in the hills near Austin and San Antonio.
Chalk is limestone, or a kind of limestone; the two terms are not interchangeable. Saint-Émilion, for example, has limestone in places; it does not have chalk. Limestone is hard: you can build cathedrals and palaces from limestone. It takes a nice sharp edge and it wears well. Chalk is soft: those tunneled cellars that honeycomb the rock under Epernay were relatively easy to dig. What is the difference between chalk and limestone? And how can they be both good and bad for vines?
All about the limestone
All limestone is sedimentary rock, composed of the remains of minute organisms which inhabited the seas millions of years ago, and there are umpteen different kinds. In Burgundy alone you'll find crinoidal limestone (crinoids were ancient sea lilies) in Le Chambertin, parts of Vosne-Romanée and parts of Clos de Tart; dalle nacrée, or pearly flagstone, formed from the shells of oysters and other bivalves, in Pommard's Clos des Epeneaux; Oxfordian limestone in Saint-Romain. In Chablis you have soft Kimmeridgian limestone, embedded with tiny comma-shaped shells, and the less-favored hard Portlandian limestone. All have different structures and chemistry.
Even chalk, itself a particular kind of limestone formed from plankton called coccoliths, can be divided into nine different formations. Ian Kellett of Hambledon values his chalk, which is called Newhaven Chalk Formation, for its structure, and reckons it is slightly better for vines than the marginally younger Tarrant Chalk Member and Spetisbury Chalk Member or the marginally older Seaford Chalk Formation, but says that the obsession that some growers have with chalk that contains large numbers of belemnite fossils is misplaced. Christian Seely of Coates & Seely says that when they had their Hampshire soil analysed in France it was confirmed to be a type particularly suited to Champagne grapes. It's a bit like people talking about their children: little Abigail is starting Mandarin lessons, and little Tarquin said the funniest thing yesterday about Nietzsche! Discussing chalk with growers unveils a whole and almost infinite new world of one-upmanship.
Levels of active lime or chalk in soils are another area where growers can sound as if they're swanking about little Abigail's progress in Mandarin: Oh, the active lime here is 25 percent. What they're referring to is the degree to which the lime (calcium oxide) has weathered out of the soil. Active limestone contains lots of lime. Very old limestone soils may have less. In the Marne Valley about 20 percent active chalk is usual. Calcium affects acidity: see below.
Chalk is good for grapes because of the way it handles water. It both drains well, so doesn't get waterlogged, and keeps the water table at a fairly consistent level. Says Kellett, "it has amazing capillary action. The combination of the plant's capillary action and the chalk's capillary action means there's a pump effectively going down 500m into the chalk." One cubic meter of chalk can hold 660 liters of water, mostly because of the way the chalk has developed minute fractures and fissures over the millennia. Other kinds of limestone are very varied, with different degrees of hardness, different structures, different ways of cracking and fissuring, and thus different levels of drainage. If it's too hard, too solid, vine roots can't penetrate it: this will not be good vineyard land. It has to weather and crack to be useful.
Iron in the soul
But plant vines on absolutely pure chalk, and sooner or later you’ll have dead vines. The leaves will yellow and wither: it’s called chlorosis, and it's caused by iron deficiency. So chalk soils that work well for vines manage to have some iron as well: Champagne has streaks and pits of lignite coal, which contains iron, and is a traditional fertilizer here; in the chalky vineyards of Sancerre, iron comes from a layer of weathered sandstone. In the terra rossa of Coonawarra, the red topsoil contains the iron that the limestone underneath lacks. You could say it's a magic combination. Even in Champagne, chalk needs clay.
Luckily for the vine, the ingredients of any given topsoil don't just come from the weathering of the rock beneath: they have been washed there, or blown there, or even dumped there by glaciers. Geological faults reveal other layers that get weathered into the soil; erosion does its slow work. Lots of those other rocks that get weathered into topsoil contain iron, though if it's not in soluble form the vine can't get at it, so there can still be a problem of chlorosis.
But what does all this mean for wine style? We associate chalk and limestone with freshness and elegance, from a combination of good drainage and water availability. Well drained soils warm up faster in spring than wet clay ones, but at the same time the paleness of the soil reflects more heat than darker soils, which absorb more heat. That balance of warmth reflected back on to grapes or absorbed by the soil can affect wine style. Says Alex Maltman in his brilliant book Vineyards, Rocks, & Soils: "The wavelength of reflected light, which depends on the colour of the ground, can affect enzyme activity and ultimately the sugar and alcohol content of the wine." The classic vineyard soil of Burgundy is argilo-calcaire: clay-limestone. There's an old rule of thumb there that black grapes suit the darker, more clay-rich soils, white grapes the paler, more limestone-rich soils.
We associate limestone with lighter tannins in reds, brighter aromas and a generally brisk feeling; such wines can be a bit lean in youth, but age well. These high-calcium, low-potassium soils seem to allow better uptake of nutrients by vine roots, while at the same time boosting acidity. Plenty of wines grown on other soils have acidity, too, but in England, where sparkling is grown on every sort of soil, there is beginning to be a feeling that chalk gives acidity that is perceived differently; that kicks in earlier on the palate and carries through more gracefully, even though the figures might be the same, than acidity from other soils. You could call it finesse.
Beyond Burgundy
Château Ausone, the epitome of elegant Bordeaux, is up on Saint-Émilion’s plateau, its cellars carved into the Calcaire à astéries ("starfish") limestone (the hardness of the rock means sharper-edged cellars than the rounded tunnels of Champagne). Cabernet Sauvignon does not ripen well up here on the limestone plateau: this is Cabernet Franc country, and Merlot of a more restrained mien.
On the other side of the river, there is limestone, but much further down, a long way under the gravel; perhaps too far to have much effect. Elegant Haut-Brion grows vines on Günz gravel over Pliocene gravel over Calcaire à astéries. Arguably other factors have a greater influence on style than the quite distant limestone. Margaux has soft Molasses du Fronsadais limestone deep under its gravel. Latour and Lafite are both on deep gravel, with limestone underneath, but Latour has more clay. I'm not suggesting that's the only reason the two wines are so different, while being geographically so close; terroir always involves a multiplicity of factors. Soil and subsoil are only part of the story, and the deeper down below the soil surface you go the more indirect are the effects.
Where else in the world does limestone whiten the topsoils and produce wines of notable elegance? Cognac has limestone; Spain’s Jerez, where the white albariza soils make sunglasses essential and produce the finest Finos, has lots; Slovenia's karst limestone produces fresh Teran reds. California has some, in parts of the Central Coast: Tablas Creek reckons its limestone-based soils are the reason it is able to grow vines without irrigation, even though it gets little rain between April and November.
And as an afterthought, if you visit Rías Baixas in northern Spain (we'll be able to go visiting again one day) you may see shellfish shells scattered in the vineyards. Yes, they farm them round the shoreline, but this is not simply a way of disposing of the remains of lunch. Nature carelessly omitted to provide limestone in these parts; clam shells, as they weather, can make up for that.
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Chalk: Wine's White Gold - Wine-Searcher
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