The Night in April

On the night of 26 April 2016, and again on 6 April 2021, growers across Burgundy stood in their vineyards among burning candles and watched the temperature fall.

The dormant vine is hardy and will survive well below freezing. The emerged green shoot will not: minus two degrees for an hour is enough to kill it, and with it the bunch it would have carried. In both those years, large fractions of the region's crop were destroyed in a night.

The cruelty of it is that warming has made this worse rather than better. Budbreak has moved earlier as springs have warmed, while the date of the last frost has not moved as much, so the window in which the vine is vulnerable has widened. A warmer climate has produced more frost damage, which is not the relationship anybody expects.

The defences are all expensive, all partial, and all worth knowing about because they say something about the economics.

The candles (bougies, tins of paraffin wax placed between the rows) raise air temperature by perhaps one to two degrees and disturb the cold layer sitting on the ground. They cost a great deal in fuel and in labour for a night that may not come, and they require somebody awake at three in the morning to light several hundred of them.

Sprinkling water sounds perverse and works: as water freezes it releases latent heat, so a bud encased in ice stays at zero rather than falling to the air temperature. It needs a great deal of water, reliable delivery, and continuous application until the thaw, and it is unavailable on most Burgundian slopes.

Helicopters mix warmer air from above down into the vineyard, which works when there is a temperature inversion and does nothing in an advective frost where the whole air mass is cold.

Then the season proper begins, and the threats change.

Powdery mildew and downy mildew both arrived from North America in the nineteenth century on imported vine material, alongside phylloxera: a set of introductions that nearly destroyed European viticulture and permanently changed how it is practised. Downy mildew thrives in warm wet conditions and attacks leaves and bunches; powdery prefers humid but not soaking weather.

Neither can be ignored, which is why organic and biodynamic growers spray copper and sulphur rather than nothing at all. A wet July is a grower's worst news after a frost, because it means spraying on a tight schedule in conditions that make the vineyard impassable.

Hail is the threat nobody can do anything about. It is uninsurable in practice in some communes, and it can destroy a crop in four minutes. Volnay and Pommard were struck in three consecutive years from 2012.

The response has been partly legal: since 2017 growers may in certain circumstances hold a reserve from one year to release in another, and estates increasingly keep stock deliberately for that purpose. The wine cannot be replaced, so the business has to be built to survive a year with nothing in it.

Between these, the season has a turning point worth knowing by name.

Until véraison, a grape berry is essentially a leaf: hard, green, photosynthesising, high in acid, growing by cell division. At véraison it changes function entirely. It softens, colours, stops producing sugar and starts importing it from the rest of the plant.

Harvest is conventionally reckoned at about forty-five days after véraison, which is why growers watch for it so closely, and its timing has moved forward by roughly two weeks since the 1980s.

And then the last three weeks, which decide vintage reputations and are almost never predictable.

Botrytis needs moisture sitting on the skins. A wet August that looks like disaster can be reversed entirely by three weeks of dry northerly wind, which dries the bunches and stops an outbreak that was about to take the crop. Several vintages written off by the trade in early September turned out well because of exactly this.

Which is why any generalisation about a vintage made before October is worthless, and why the people who make them anyway are usually selling something.