Sémillon (Botrytised)

Sauternes is the benchmark for botrytised sweet wine, and Sémillon is the grape that makes it possible. The commune sits at the confluence of the Ciron and the Garonne, south-east of Bordeaux, and the geography is the whole explanation: the cold spring-fed Ciron meets the warmer Garonne and generates autumn mists that sit over the vineyards each morning, burning off under afternoon sun.

That exact alternation — damp then dry — is what Botrytis cinerea needs to develop as noble rot rather than destructive grey rot. Sémillon's thin skin makes it unusually receptive to the fungus, far more so than the Sauvignon Blanc and Muscadelle that make up the rest of the blend.

The rot punctures the berry, water evaporates, and sugar, acid and glycerol concentrate. The grape shrivels to something unattractive and brownish that produces one of the great wines of the world. Pickers go through the vineyard repeatedly over weeks, taking only berries at the right stage, and yields are famously tiny — the often-quoted figure at Château d'Yquem is roughly one glass per vine.

The wine is golden, viscous and long-lived, with apricot, honey, candied orange, saffron and a distinctly waxy, lanolin note that is Sémillon's own. New oak barrel fermentation adds vanilla and toast. Acidity keeps it from collapsing into sugar, and the best examples improve for half a century, darkening towards amber and developing dried fruit, caramel and barley sugar.

Barsac, Monbazillac and Australia's Riverina make related wines from the same grape.