Champagne's bubbles are made by chalk, twice

Champagne is the only great wine region whose most famous feature is a geological accident used twice. The chalk under the vineyards grows a grape that is almost undrinkable on its own, and then the same chalk, hollowed out, provides the one environment in which that grape can be turned into something worth opening. Two jobs, one material, and neither of them is romantic.

The grape the north can grow

Champagne sits at about 49 degrees north, which is the edge of what Europe can do with wine. The growing season is cool and short; the grapes ripen to a sugar level that would make a still wine thin and sharp. What they do have is acid — a lot of it, with a pH that can sit near 3.0. In a warm region, acidity is a problem to be corrected. Here it is the raw material.

The soil explains why the acid tastes of anything at all. The chalk is soft, highly porous and poor: it drains water fast, so the vines root deep and struggle, and a struggling vine puts its energy into concentration rather than into leaves. That is the first job. A vine planted on deep fertile soil makes a lot of wine that tastes of very little.

The second fermentation is the wine

A still Champagne is a sharp, thin white. What turns it into champagne is a second fermentation inside the closed bottle: a little sugar and yeast are added, the yeast eats the sugar, and the carbon dioxide it produces has nowhere to go. The pressure climbs to about six bar — roughly three times the pressure in a car tyre — which is why the bottle is thick and the cork is held on with a wire cage.

Then the wine sits on the dead yeast. This is the part that takes time and cannot be rushed: the yeast cells break down and release compounds that taste of brioche, cream and toasted bread. The rules ask for fifteen months on the lees for a non-vintage and three years for a vintage. Those months are not ageing in the sense of mellowing; they are a chemical extraction that only runs at a certain temperature.

The cellar is a machine with no moving parts

Thirty metres of chalk has enormous thermal inertia. It does not hold a temperature because it is cold; it holds one because changing it would take months. A crayère sits at 10 to 12 °C in January and at 10 to 12 °C in August, which is exactly the band in which a second fermentation proceeds slowly enough to leave the lees intact and the bubbles fine. A cellar with seasons would stall the fermentation in winter and race it in summer.

The chalk's second contribution is humidity. It is porous, so it holds water and releases it, keeping the galleries near 90 per cent. That matters because a dry cellar evaporates wine through the cork and dries the cork itself; a chalk cellar keeps both.

And here is the detail that makes the whole thing feel accidental. The crayères were not dug to store wine. They were quarries. The chalk was taken out for building stone — for the Roman city, for the medieval cathedral, for the houses above — for the better part of two thousand years. The wine industry inherited the holes. Reims is a city built out of the material that now ages its wine, and the cellars are the negative space of the buildings.

The legend runs backwards

The story everyone knows is that a monk named Dom Pérignon invented champagne by accident, and the region has been grateful ever since. The documents point the other way. Dom Pérignon spent his career at Hautvillers trying to keep bubbles out of the wine, because in the seventeenth century a refermenting bottle was a defect and a hazard: the glass of the period exploded in the cellar often enough to be called "the devil's wine".

What he actually did was more useful and less quotable: he worked on blending — pressing different parcels separately and combining them — and on clarifying the wine, and on the practice of picking early to keep acidity. All of that is the foundation of the champagne method. The bubbles were not the invention; the control was.

How to taste the chalk

Two things to look for, and both are structural rather than flavour. First, the acidity: a champagne should feel sharp at the edges and clean through the middle, not soft. That sharpness is what a cool region does and what the second fermentation does not remove. Second, the length of the lees character — the brioche note should sit behind the fruit, not on top of it, and it should last after you swallow. A wine that tastes of bread and nothing else has been dosed for the market, not aged for the cellar.

Serve it at 8 to 10 °C, in a glass wide enough to smell, and the chalk will read as a texture rather than a flavour: a kind of dry, chalky grip at the back of the mouth that no warm-climate sparkling wine reproduces.

This is entry 02 of Land & Terroir in About France. The pillar's argument — that France wrote soil and weather into law — is set out on the pillar page.