What is Noble rot?

Noble rot is the beneficial form of a grey fungus, Botrytis cinerea, affecting wine grapes. Infestation by Botrytis requires moist conditions. If the weather stays wet, the damaging 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 is known as noble rot. Grapes picked at a certain point during infestation can produce particularly fine and concentrated sweet wine. Wines produced by this method are known as botrytized wines.