Noble Rot

How it works

The fungus needs a specific sequence of conditions. First, the grapes must be ripe. Then a period of humid weather, usually foggy mornings, allows the fungus to establish on the skins. Then a period of dry, warm weather concentrates the grapes, desiccating them on the vine. The cycle of humidity and dryness can take several weeks, and the resulting grapes look awful, shrivelled and brown, but the juice is intensely sweet and flavourful.

The chemistry is complex. The fungus consumes some of the grape's acids and produces glycerol, which adds body. It also produces enzymes that break down the cell walls, releasing aromatic compounds. The result is a juice with very high sugar, often 25 to 35 percent potential alcohol, balanced by high acidity and a unique aromatic profile of honey, beeswax, apricot, marmalade and saffron.

The destructive alternative

Grey rot, the bad form of Botrytis, happens when the fungus establishes without the drying cycle. The grapes collapse into a wet, mouldy mass, often with off-aromas of vinegar and rot. Grey rot is a constant threat in the UK climate, where autumn damp can be persistent. Most UK growers dread Botrytis, because it usually appears in the destructive form.

Achieving noble rot in the UK is a rare and unpredictable event. A few warm, dry autumns have produced small quantities of botrytised wines from Bacchus, Ortega and Chardonnay, but the volumes are tiny and the conditions are hard to repeat.

Noble rot in the UK

English noble rot is a small but celebrated category. The most famous example is from Nyetimber, which has made a small quantity of a botrytised Chardonnay called 1086 Rosé. Chapel Down has made a botrytised Bacchus, the Vin Doux. Ridgeview and Hambledon have also produced small batches of late-harvest wines from botrytised fruit.

The biggest UK project in the noble rot space is the Three Choirs Vineyard in Gloucestershire, which has produced botrytised wines for decades. East Anglian producers, including Winbirri, have made a botrytised Bacchus. Volumes are small, often only a few hundred cases, and the wines are released at a premium price.

Sauternes and the global benchmark

The benchmark for noble rot wines is Sauternes, the French region south of Bordeaux, where the climate and the Sémillon, Sauvignon Blanc and Muscadelle grapes combine to produce the world's most famous botrytised wines. Chateau d'Yquem is the most prestigious, with wines that can age for a century or more. Other Sauternes producers include Château Suduiraut, Château Coutet and Château Rieussec.

The Tokaji Aszú wines of Hungary are the other global benchmark, made from botrytised Furmint and Hárslevelű grapes. Tokaji Eszencia, the rarest form, can be almost syrupy, with hundreds of grams of residual sugar per litre. German Auslese, Spätlese and Trockenbeerenauslese wines can also be botrytised, although the proportion is much smaller.