Noble Rot vs Grey Rot
Botrytis cinerea is the same fungus whether it appears as beneficial noble rot or destructive grey rot — the difference lies entirely in timing and conditions. Noble rot requires a specific microclimate: morning mists or fog followed by warm, dry afternoons. The moisture encourages the fungus to penetrate the grape skin, then the sun desiccates the berries. If conditions remain wet, the fungus destroys the crop as grey rot.
How Noble Rot Works
- Infection — Botrytis spores land on thin-skinned ripe grapes (Sémillon, Furmint, Riesling, Chenin Blanc)
- Penetration — microscopic filaments pierce the skin, creating tiny perforations
- Desiccation — water evaporates through the perforations, concentrating sugars to 30–40% (vs. normal 20–24%)
- Flavour transformation — the fungus metabolises acids and creates unique compounds: sotolon (honey, caramel), phenylacetaldehyde (honeyed), and glycerol (viscosity)
Great Botrytis Wines
- Sauternes (Bordeaux) — Sémillon-dominant; Château d'Yquem is the archetype
- Tokaji Aszú (Hungary) — Furmint-based; rated by puttonyos (sweetness levels)
- Trockenbeerenauslese (TBA) (Germany/Austria) — Riesling; rarest German Prädikat level
- Quarts de Chaume & Bonnezeaux (Loire) — Chenin Blanc; Loire's noblest sweet wines
- Beerenauslese (Germany/Austria) — less concentrated than TBA but still intensely sweet
Harvest Challenges
Botrytised grapes must be hand-harvested in multiple passes (tries) as the fungus affects berries unevenly. A single harvest can take weeks. Yields are tiny — often just one glass per vine — explaining the high cost of these wines.