Botrytis (Noble Rot)

What is Botrytis?

Botrytis cinerea is a fungus that, under specific climatic conditions, attacks wine grapes and triggers a fascinating transformation. While the fungus can wreak devastating damage as "grey rot" in humid conditions, under ideal circumstances it develops into so-called noble rot (French: pourriture noble) – the key to the world's most precious sweet wines.

How Does Noble Rot Develop?

The development of Botrytis into noble rot requires a specific microclimate:

Ideal conditions

• Morning mist or humidity: Allows the fungus to adhere to and grow on the grapes
• Warm, dry afternoons: Cause the berry skins to shrivel and concentrate the grape juice
• Late autumn: Fully ripe grapes with high sugar content
• Alternating humid and dry conditions: Prevents aggressive grey rot

These conditions are found particularly along riverbanks (e.g. the Mosel, Sauternes on the Garonne) or in regions with morning mist and afternoon sunshine.

The Transformation Process

The Botrytis fungus penetrates the berry skin with microscopic hyphae (fungal threads) and triggers several chemical changes:

1. Water evaporation: The berries lose up to 80% of their water and shrivel into raisin-like forms
2. Sugar concentration: The remaining juice becomes extremely concentrated, with sugar levels of 30–40% (normal: 15–25%)
3. Acid reduction: Natural acidity is partially broken down, which contributes to the balance
4. Aroma development: New, complex aromas emerge – honey, dried apricots, botrytis notes

The result: a highly concentrated, aromatically complex must that is vinified into exceptional sweet wines.

Famous Botrytis Wines

Sauternes & Barsac (Bordeaux)

The sweet wines of Sauternes, above all Château d'Yquem, are the ultimate expression of noble-rot wines. The primary grape Sémillon is particularly susceptible to Botrytis and develops intense honey, apricot, and saffron aromas.

Trockenbeerenauslese (Germany)

German Riesling Trockenbeerenauslesen are among the rarest and most expensive wines in the world. These concentrated, nobly sweet wines from the Mosel, Rheingau, or Pfalz combine extreme sweetness with vibrant acidity.

Tokaji Aszú (Hungary)

The legendary Tokaji from Hungary is made from noble-rot-affected Furmint and Hárslevelű grapes. The Aszú berries are harvested separately and added to the base wine – the more Puttonyos, the sweeter the wine.

Vendanges Tardives & SGN (Alsace)

Extraordinary sweet wines are produced in Alsace from noble-rot-affected Gewürztraminer, Riesling, and Pinot Gris. The Sélection de Grains Nobles (SGN) is the Alsatian equivalent of the German Trockenbeerenauslese.

Harvest & Winemaking

Harvesting botrytis-affected grapes is extremely labour-intensive:

• Selective hand harvesting: Only fully noble-rot-affected berries are picked
• Multiple passes through the vineyard: As noble rot sets in unevenly, 3–6 passes are required
• Low yields: From 100 kg of grapes, often only 5–10 litres of wine are produced (normal: 60–70 litres)
• Slow fermentation: The high sugar content impedes fermentation, which can take months

This demanding production process explains the high prices of Botrytis wines.

Flavour Profile

Wines made from noble-rot-affected grapes display a unique aromatic profile:

Primary aromas

• Dried apricots and peaches
• Honey and beeswax
• Raisins and candied fruit

Secondary aromas

• Orange marmalade
• Saffron and exotic spices
• Nuttiness (almonds, hazelnuts)

Botrytis note

A characteristic, hard-to-describe scent – often described as "noblely fungal", "waxy", or "honey-wax-like". This typical Botrytis note makes the wines unmistakable.

Grey Rot vs. Noble Rot

Not every Botrytis infection is desirable:

Grey rot (Botrytis rot)

• Occurs in persistently humid weather
• Destroys the grapes completely
• Leads to musty, unpleasant aromas
• Causes crop loss

Noble rot (Botrytis noble)

• Develops in an ideal alternation of humid and dry conditions
• Concentrates sugar and aromas
• Creates complex, honeyed notes
• The foundation for world-class sweet wines

Winemakers must monitor the weather closely to walk the narrow line between noble rot and grey rot.

Ageing Potential

Botrytis wines are among the longest-lived wines in the world:

• 20–30 years: Trockenbeerenauslesen, Sauternes
• 50–100+ years: Château d'Yquem, top Riesling TBA
• Development: With age, the wines darken (amber to mahogany) and develop complex tertiary aromas such as caramel, nuts, and dried fruit

The high concentration of sugar, acidity, and extract preserves the wines naturally.

Conclusion

Botrytis cinerea is a fascinating example of how nature can turn a potential pest into an enrichment. Noble rot transforms ordinary grapes into liquid gold and enables sweet wines of unrivalled complexity and elegance. Every sip of a noble-rot wine is a gift from nature – rare, precious, and unforgettable.