Botrytis cinerea, a.k.a. noble rot, is a type of fungus that attacks the skin of grapes, causing the water to evaporate and dramatically increasing the sugars and flavors (essentially turning a grape into a big raisin). This is disastrous for red grapes, as it ages them prematurely. But when the climatic conditions are exactly right, the effect of Botrytis cinerea on white grapes creates an incredibly concentrated, sweet grape juice that's turned into the finest—and most expensive— dessert wines in the world. In fact, it may take an entire vine just to make one glass. The Sauternes from France are a classic example, as are German Trockenbeerenauslese [TROCK-en-BEER-in-OUSE-lay-sin] wines, though Botrytis cinerea affects vineyards all over the world.