thumb|Noble rot on [[Riesling grapes (Rheingau, Germany, 2005)]]
Noble rot (; ; ; ) is the beneficial form of a grey fungus, Botrytis cinerea, affecting wine grapes. Infestation by Botrytis requires warm and humid conditions, typically around and above 80% humidity. If the weather stays wet, the undesirable form, "bunch rot" or "grey rot", adversely affects winemaking by disrupting fermentation and changing the taste, aroma, and appearance of the final wine. and are considered a distinct category of dessert wines. Significant differences are also evident in other components, like sugar alcohol and acid composition, due to microbial activity. Additionally, a notable feature of botrytized wines is their high acid content, which prevents them from tasting cloying, even with sugar levels often exceeding 200 g/L. When vineyard classification began in 1730 in the Tokaj region, one of the gradings given to the various terroirs centered on their potential to develop Botrytis cinerea.
There is a popular story that the practice originated independently in Germany, where the Riesling producers at Schloss Johannisberg (Geisenheim, in the Rheingau region) traditionally awaited the say-so of the estate owner, Heinrich von Bibra, Bishop of Fulda, before cutting their grapes. In 1775, the story claims the abbey messenger was robbed en route to delivering the order, delaying cutting by three weeks, time enough for the botrytis to take hold. The grapes were presumed worthless and given to local peasants, who produced a surprisingly good, sweet wine which became known as Spätlese, or late harvest wine. In the following few years, several different classes of increasing must weight were introduced, and the original Spätlese was further elaborated, first into Auslese in 1787 and later Eiswein in 1858 (although Eiswein is usually made from grapes not affected by Botrytis).
Viticulture and uses
thumb|Botrytis cinerea on [[Sémillon grapes in Sauternes]]
In some cases, inoculation occurs when spores of the fungus are sprayed over the grapes, while some vineyards depend on natural inoculation from spores present in the environment.
Botrytized wines can be made using many varieties of grape. Due to anthocyanin oxidation, a majority of varieties are white. The ideal varieties mature late in the season in order for ripening to coincide with the best environmental conditions for noble rot to occur. Thick skinned cultivars can also be used to make harvesting infected grapes less difficult. Riesling and Sémillon are the primary cultivars used in the production of botrytized wines. The Hungarian variety, Furmint, is the predominant variety used in the production of Tokaji Aszú. Other varieties, such as Picolit, Gewürztraminer, Chenin blanc, and Pinot blanc, are used, depending on tradition and adaptation to local conditions.
Some of the finest botrytized wines are picked berry by berry in successive (French for "selections").
Internationally renowned botrytized wines include the aszú of Tokaj-Hegyalja in Hungary (commonly called Tokaji or Tokay),