What is Chalk?

Strap in for the When, Where, What and Why of the white stuff.

'Belemnite’ fossils in the Sedgwick Museum in Cambridge. These are extinct cephalopods that had a tube-like skeleton. Above are the ‘Actinocamax’, found across the Cretaceous period. To the far right of the picture are some Belemnitella Mucronata found in the Upper (more recent) Cretaceous, and especially the Upper Campanian chalk typical of Champagne’s Grand Crus.

Chalk. When I started my journey into sparkling wine (including by following the nascent English wine industry), I didn’t really understand what the fuss was about. Were wines on chalk soils supposed to taste chalky?

Nobody has shown that the flavour of chalk, or soil or mineral of any kind, directly enters wine through the vine’s root system and into the grapes. It just doesn’t happen. Yet wines from a very shallow topsoil over chalk bedrock seem to show a distinct character; stony, restrained, long, buzzing, whereas wines from deeper topsoils (even just metres away, vinified in exactly the same way), show rounder, more fruity characters.

Some of the time, at least. Often enough, though, for even for someone with a natural cynicism towards simplistic wine trivia to admit something’s up.

It’s one of the most compulsively brilliant, beautiful and beguiling puzzles in Champagne, and part of me hopes that nobody ever quite ‘solves’ it. What we can do, though, is have a serious geek-out. First, I’d recommend a recap on Champagne’s soil formations with the help of some plasticene:

Video - Champagne's Geology

Then, onto when chalk formed, where it appears, what is actually is and what (we think we know) it does for wine.

(Also, a gentle reminder that we’re ringing in the festive season in London a week today (14th Nov) with a knockout wine and food evening at Oeno Maris….come!)

Oeno Maris and the best of English Sparkling Wine

1. When

The chalk of Champagne formed during the Late Cretaceous period of the Mesozoic era (the last dance of the Dinosaurs before the K-T extinction event and the ‘Tertiary’ era began).

Northern Europe was underwater, and, as the plankton in the seas died, they settled to the bottom, broke apart and their calcium carbonate remains (coccoliths) formed sedimentary rocks in which other sea creatures (such as Belemnitella Mucronata, Actinocamax, and Micraster Coranguinum) were also fossilised.

The chalks of the Upper (later) Cretaceous Period:

2. Where

The chalk is everywhere in Champagne - but only in places is it near enough the surface to affect the vineyard.

As the video on Champagne’s Geology shows, the older the chalk, the lower down the sedimentary layers it lies and the further East/Southeast it crops out at the surface in Champagne. This is because the chalk layers were lifted up as the Paris Basin sank, exposing the oldest layers furthest from the centre of the depression. It’s also why you often see the Upper Campanian chalk at the top of the slopes just under the boundary with the Tertiary sands and clays, and then the Lower Campanian and Santonian as you descend.

Here’s an example from the Grand Cru village of Bouzy on the Southern face of the Montagne de Reims:

The chalk in Champagne is located near the surface all around the slopes of Montagne de Reims (but not the Petite Montagne, west of Villers-Allerand), the Grande Vallée from Mareuil-sur-Aÿ out to Damery, and the Côte des Blancs (where the vineyards are largely planted on the East-facing ‘Escarpment’ of the ‘Cuesta’ - as below (although the Santonian in the Côte des Blancs is way down the slope, out of the range of most of the villages):

What?

Chalk is a kind of limestone, which is to say that it is a rock formed from the sedimentary deposition of marine creatures.

Chalk is formed by coccoliths, detached plates of calcium carbonate that were once part of the plankton that swarmed the ‘Tethys’ ocean. Below you can see the spherical plankton still intact, and the coccolith discs that have detached.

Over time these compress and form a very pure calcite (calcium carbonate) rock called chalk. When the seas receded, earthquakes and the Paris Basin depression brought this chalk to the surface, capped by later deposits of sands and clays from the Paleogene period. Being fairly soft, it weathers easily and forms the characteristic smoothed-out hills of Champagne or the North and South downs in England.

The terms ‘Belemnite’ and ‘Micraster’ are traditionally heard in Champagne to mark out the chalks of the Upper Campanian (viewed traditionally as superior) and the Santonian (viewed as inferior). These two types of creature - Belemnitella a type of squid-like cephalopod and Micraster an echinoid - are found fossilised in the respected layers. The chalk is not made out of them.

Changes in the composition of chalk across Champagne are more to do with the balance of other microscopic creatures (such as foraminifera), siliceous (silica-based) materials such as flint (which is often found bedded in chalk, derived from siliceous organisms also living in the seas), and other minerals. Winemakers will spin you tales about what their exact type of chalk does differently, but - with a few exceptions, as we’ll see - there’s little in the way of consistent vinous data here.

Chalk is not the soil

As Geologist Alex Maltman points out in Vineyards, Rocks & Soils, it is the soil, not the bedrock that provides most of the water and nutrition for the vine. Maltman is inclined to be a terroir-sceptic, but he has a point: chalk is a foundation for a vine, but not its bricks and mortar.

Soil, though, is very difficult to map; it moves, it undulates, it comes from winds, rivers, erosion, gravity. Most of all, it interacts with humans: it’s here that the ‘life’ of the soil exists, and here that - chalk or no chalk - Champagne’s vignerons have their work cut out in avoiding compaction and lifelessness.

What that means, then, is that trying to draw conclusions about how wines change based on the boundaries of one type of geologic bedrock or another is largely a wild goose chase without considering the soil on top, let alone different climatic or physical conditions. The old adage in Champagne is that the Santonian chalk is inferior for viticulture, but is that because of the quality of the chalk itself, or the fact that is is found down toward the plains, where topography is also less suitable (i.e. flatter and more frost-prone)? It’s here that the chalk talk enters the realm of the highly speculative.

Why?

What does chalk actually do in Champagne?

Waterworks

Chalk is an aquifer - it stores water. And it stores a lot, too; up to 400 litres per cubic metre. This is partly due to the natural porosity (the millions of tiny gaps between particles) of the material, but also, as Maltman believes, down to “microfissures in the rock - it’s an excellent example fracture porosity and permeability”.

Effectively chalk is a useful buffer - Vines that root on, or into, chalk, draw up water which rises through capillary action; even in a drought, they may still get access to water, preventing hydric stress (which can be especially negative for sparkling wine wines, although some is usually desired for still wine production). In intense rainfall, too, the chalk can draw away water, preventing the soil from becoming waterlogged and choked (which, as we saw in parts of Champagne in 2024, can block the vine’s access to nutrients),

The reality, on the ground, though is often more complicated; there are plenty of wines from chalky Grand Crus that still showed the effects of hydric stress in the 2015 vintage, for example - even if their winemakers are keen to point out how well protected they were by the chalk!

Texture

Mariagiovanna Basile puts together bespoke maps of Champagne villages showing vineyard lieu-dits and soil types at her website ‘Enographiae’. Here’s an example from Villers-Marmery and Trépail on the Eastern flank of the Montagne de Reims:

An architect by trade, she developed a fascination with Champagne’s terroir that kick-started a mapping project of formidable complexity. She’s keen to point out that the texture of the chalk might be more important than the exact age of it:

“Chalk is not just a block - it’s not what we learnt at school”, she explains. “It can be broken up, or in little grains, or with marnes, silex….if you don’t understand that when you look at a map and you see ‘Chalk with Belemnites’ you might think it’s all the same.”

At Domaine La Rogerie in Avize - a village legendary for a 100m-deep bed of belemnite chalk - François Petit agreed it seemed as though his vineyards on more fragmented bedrock showed a more pronounced mineral, chalky character as the vine’s roots are able to descend more easily. Indeed a number of vignerons have told me that when vines encounter hard, unbroken chalk bedrock they simply remain in the topsoil, spreading over the top of the chalk like a creeper covering a stone and getting less benefit from the chalk’s hydric reservoir. Although, again, others (such as Jean-Baptiste Lécaillon), disagree….

Other effects of calcareous soil

Calcareous (calcium-rich) soils are high pH. When I tested a topsoil on the North Downs near Canterbury in Kent, it came back at 8.2: Vitis vinifera roots can cope with this, but the rootstocks developed with American vines to combat phylloxera (onto which Champagne’s vine varieties are grafted) struggle to take up iron in these conditions; only 41B and Fercal rootstocks are suitable for high Calcium Carbonate levels, so Champagne is largely planted on these.

Calcium in soils helps them flocculate - structure themselves in small clumps - which improves aeration, and therefore microbial activity… and therefore ‘Cation Exchange Capacity (the ability of the soil to transmit nutrients).

Generally winegrowers observe that vines grown on calcareous soils produce wines with lower pH than in other soils. Low pH is generally accepted as a desirable trait in sparkling wines, as it tunes to wines toward brightness and freshness, and increases their longevity. The science for this is still emerging: it appears that increased calcium prevents excessive potassium levels in the grapes. Potassium can drive up pH by precipitating out with tartrates and malates, taking hydrogen ions (the ‘H’ in pH), out of the picture.

Finally there is some evidence to suggest that high calcium can strengthen grape skins, further protecting them against fungal disease. Some growers actually spray calcium products.

The Lowdown

Taken together, the effects of a high pH, calcium in the topsoil, unique hydrology and a dash of we-don’t-quite-know-yet, seem to add up to something tangible. I love the driving length, the slight strictness, the sense of compressed energy that can leap out from wines that capture it.

If you want to do some direct comparisons of nearby parcels that show shallow, chalky profiles (left) versus deeper, richer ones (right) made by the same people, here are some wines (sorry they’re a bit pricy, but this is sharp-end of Champagne’s terroir movement…)

Pierre Peters - Les Chétillons vs Les Montjolys

Philipponnat - Le Leon vs Mareuil-sur-Aÿ

Larmandier-Bernier - Latitude cs Longitude

Agrapart - Mineral vs Avizoise

Girard-Bonnet - Au Bout du Chemin vs Mon Village