Wines produced in the region of Barsac, such as "Premiers Crus" Château Climens and Château Coutet are allowed to be labeled either with the commune name or with Sauternes. The intense sweetness is the result of the grapes being affected by "Botrytis cinerea", a fungus that is commonly known as noble rot. In the autumn, the Ciron river produces mist that descends upon the area and persists until after dawn. These conditions are conducive to the growth of the fungus which desiccates the grape and concentrates the sugars inside. The three main grapes of this area are Sémillon, Sauvignon blanc and Muscadelle.