Noble Rot

Noble rot is the name for Botrytis cinerea when it works in the winemaker's favour. The Australian Wine Research Institute describes Botrytis cinerea as the fungus that causes the grapevine diseases botrytis bunch rot and grey mould. Vins de Bordeaux explains that in the right climatic conditions it attacks very ripe, thin-skinned grapes, which start to shrivel like raisins, and that the fungus changes the entire metabolism of the grape. When its spores germinate, they grow filaments whose tips exude an enzyme that dissolves tiny holes in the berry's skin. Water evaporates through these openings, concentrating the grapes' acids, sugars and flavours.

• Botrytis can be destructive or beneficial: the same fungus causes botrytis bunch rot and grey mould
• Filament tips exude an enzyme that dissolves tiny holes in the berry's skin, and the filaments also work through any cracks
• A Decanter feature by Jeff Cox states that more than half the water inside each berry is lost to the rot and the sugar inside doubles in concentration; a Vins de Bordeaux article puts the loss at up to half of the liquid inside the grapes
• The rot metabolises the acids along with a bit of the sugar, and excretes glycerol, which contributes to the silky mouthfeel of the wines

Noble rot depends on a daily cycle in autumn. Lakes or rivers create misty, humid mornings that trigger the rot's bloom, and the spores attack the skin through microscopic fissures. Warm, sunny and dry afternoons then halt the spread of the rot and let water in the grapes evaporate through the pierced skin, concentrating sugars, flavours and aromas. Should damp conditions persist, the berry degrades instead. Vins de Bordeaux describes this process as repeating on a daily basis during the autumn in specific wine regions.

• Misty, humid mornings, created by nearby lakes or rivers, trigger the fungus
• Warm, sunny and dry afternoons halt the spread of the rot while ripening continues
• Thin-skinned varieties with tight clusters suit noble rot best; in Bordeaux the most ideal variety is Semillon
• Noble rot spreads berry by berry at varying pace, so producers who can afford it handpick in several passes through the vineyard

In Sauternes, the cool waters of the Ciron River flow into the Garonne, and the combination of morning fog and afternoon sunshine creates the conditions for noble rot. In Tokaj in northeastern Hungary, the Bodrog and Tisza rivers generate humid mornings, and sunny afternoons follow. In Germany, WSET notes that noble rot is essential for Trockenbeerenauslese and that most Beerenauslese wines are botrytized. In Alsace, a semi-continental climate with very little rain and remarkable autumn sunshine favours noble rot. Wines of Germany recounts the legend that in 1775 the rider carrying the harvest authorisation to Schloss Johannisberg in the Rheingau was delayed for a couple of weeks; the grapes were found shrivelled and covered in noble rot, and that delay gave birth to Spätlese and late harvest wines.

• Sauternes makes only sweet white wines: Sémillon is the local star grape, with Sauvignon Blanc, Sauvignon Gris and Muscadelle in the blends
• Tokaj's key grapes are Furmint, the most widely planted, Hárslevelű and Sárga Muskotály (Muscat Blanc à Petits Grains); WSET calls Tokaj one of the world's first officially classified wine regions
• In Germany, some Auslese wines may be affected by noble rot, most Beerenauslese wines are botrytized, and noble rot is essential for Trockenbeerenauslese
• Alsace's Sélection de Grains Nobles comes from grapes with noble rot where the driest berries are kept, and can only be sold after ageing for 18 months

Botrytis infuses the grapes with its own set of aromatic compounds, which Decanter says can include honey, marmalade, ginger and beeswax. Vins de Bordeaux reports that noble rot wines exhibit higher levels of a fragrant aroma compound called phenylacetaldehyde. The fungus also injects an enzyme, laccase, that turns the juice golden and reduces bitterness and astringency; as the sugars oxidise, they produce honey, apricot and caramel flavours. In Sauternes, young wines show citrus, white flowers and orchard fruit, and time reveals spices, tropical fruit, nuts, and dried and candied fruit.

• Botrytis aromas can include honey, marmalade, ginger and beeswax
• Noble rot wines exhibit higher levels of the aroma compound phenylacetaldehyde
• Laccase turns the juice golden and, as the sugars oxidise, yields honey, apricot and caramel flavours
• Tokaji wines combine intense sweetness with vibrant acidity, and many Tokaji wines, especially Aszú and Eszencia, improve with age over decades

Vins de Bordeaux counts 27 Sauternes châteaux ranked in the 1855 classification, among them the one and only Premier Cru Supérieur, Château d'Yquem, and notes that Sauternes wines are the only white wines included in that classification. In 1936, Sauternes was one of the very first French PDOs to be officially recognised. In Tokaj, Decanter reports that the first written records of the Aszú method trace back to 1571. Decanter notes that making naturally botrytized wine can be costly and extremely labour-intensive, as it demands careful, manual selection in the field, and Vins de Bordeaux states that one entire vine makes only one glass of botrytized wine.

• Château d'Yquem is the one and only Premier Cru Supérieur among the 27 Sauternes châteaux ranked in the 1855 classification
• Sauternes was one of the very first French PDOs to be officially recognised, in 1936
• Decanter reports that the first written records of the Aszú method trace back to 1571
• WSET (2024) explains that Tokaji Aszú sweetness was traditionally measured in puttonyos, baskets of botrytised grapes added to a barrel of wine

Noble rot and grey rot come from the same fungus: Botrytis can be destructive or beneficial. When Botrytis ruins a crop in a protracted period of wet, cool weather, it is called bunch rot or grey rot; when wet mists are followed by dry, sunny afternoons, it becomes noble rot. Vins de Bordeaux describes grey rot or bunch rot as destructive fungal diseases caused by excessive moisture throughout the day, which can cause severe crop losses. The Australian Wine Research Institute notes that in years conducive to disease development, substantial economic loss can occur from a reduction in yield and a downgrade in fruit quality.

• Noble rot: misty mornings followed by dry, sunny afternoons
• Grey rot: a protracted period of wet, cool weather, or excessive moisture throughout the day
• Warm, sunny afternoons dry the grapes off and prevent grey rot from gaining a foothold
• Producers may risk insufficient onset, or no botrytis at all, when the weather is less ideal

Primary sources: https://www.bordeaux.com/en/mag/blog/what-is-noble-rot/, https://www.bordeaux.com/en/designations/graves-sauternes/sauternes/, https://www.bordeaux.com/en/mag/blog/the-sweet-wines-of-bordeaux/, https://www.bordeaux.com/en/mag/blog/the-secrets-of-sauternes/, https://www.wsetglobal.com/knowledge-centre/blog/2024/tokaji-decoded-the-science-behind-hungary-s-iconic-sweet-wines, https://www.wsetglobal.com/knowledge-centre/blog/2025/decoding-german-riesling-a-guide-to-quality-and-styles, https://www.vinsalsace.com/en/gouts-et-couleurs/aoc/selection-de-grains-nobles/, https://www.winesofgermany.com/our-regions/highlight-of-wine-culture/308/schloss-johannisberg, https://www.awri.com.au/industry_support/viticulture/pests-and-diseases/botrytis/. Secondary sources: https://www.decanter.com/learn/botrytis-noble-rot-explained-474590/, https://www.decanter.com/learn/whats-the-difference-between-sauternes-and-tokaji-aszu-ask-decanter-472562/, https://www.decanter.com/features/botrytis-affected-grapes-produce-some-alluring-wines-246855/. Last verified 2026-09-28