By Harold McGee
The noble rot (French pourriture noble, German Edelfäule) Botrytis cinerea is also known as bunch rot, and it is mainly a destructive disease of grapes and other fruits. It becomes noble only in the right climatic conditions, when the initial infection in humid weather is followed by a dry period that limits the infection. In this situation, the mold does several useful things. It perforates the skin of the grape, thus allowing it to lose moisture and become concentrated during the subsequent dry period; it metabolizes some of the tartaric acid at the same time that it consumes some of the grape’s sugars, so the balance between sweetness and acidity doesn’t suffer; it produces glycerol, which lends the eventual wine an incomparably dense body; and it synthesizes a number of pleasing aroma compounds, notably the maple-sugar-like sotolon, mushroomy octenol, and a number of terpenes. The honeyed flavor of these wines can develop in the bottle for decades.