Noble rot (French: pourriture noble; German: Edelfäule; Italian: Muffa nobile; Hungarian: Aszúsodás) is the benevolent form of a grey fungus, Botrytis cinerea, affecting winegrapes. Infestation by Botrytis requires moist conditions. If the weather stays wet, the malevolent form, "grey rot," can destroy crops of grapes. Grapes typically become infected with Botrytis when they are ripe. If they are then exposed to drier conditions and become partially raisined this form of infection brought about by the partial drying process is known as noble rot. Grapes when picked at a certain point during infestation can produce particularly fine and concentrated sweet wine. Some of the finest Botrytized wines are literally picked berry by berry in successive tries (French for "selections").
According to Hungarian legend the first aszú (a wine using botrytised grapes) was made by Laczkó Máté Szepsi in 1630. However, mention of wine made from botrytised grapes had already appeared in the Nomenklatura of Fabricius Balázs Sziksai, which was completed in 1576. A recently discovered inventory of aszú predates this reference by five years. 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.
A popular myth is that the practice originated independently in Germany in 1775, 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 this year (so the legend goes), the abbey messenger was robbed en route to delivering the order to harvest and the cutting was delayed for 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 subsequently 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).