Noble rot, also known as "Botrytis cinerea," is a condition in grapevines caused by the fungus of the same name. This unique form of fungal infection can be beneficial under specific circumstances, particularly in the wine-making industry. Noble rot is most famously associated with the production of certain sweet wines, such as Sauternes from France and Tokaji Aszú from Hungary.

When the Botrytis cinerea fungus infects the grapes under favorable conditions – typically involving misty or humid mornings followed by dry, sunny afternoons – it causes the grapes to partially dehydrate while still on the vine. This dehydration process concentrates the sugars and acids in the grapes, leading to a higher sugar content in the resulting juice. The fungus also imparts distinct and complex flavors to the grapes, often described as honeyed or with notes of ginger, saffron, and citrus.

Wines made from grapes affected by noble rot are often characterized by their richness, complexity, and balance of sweetness and acidity. They are typically sweet dessert wines, highly prized and often command high prices. However, the development of noble rot is a delicate balance, as too much humidity can lead to destructive grey rot, which ruins the grapes and is undesirable for wine production.