A fungus or mold that causes grapes to shrivel and become very concentrated. Also called the "Noble Rot," it is a desirable condition and causes ripe grapes to shrivel, resulting in the remaining juice becoming very concentrated. Such nobly rotted grapes yield the honeyed richness of many classic dessert wines like French Sauternes, German Trockenbeerenauslese, and Hungarian Tokaji. Conditions are right for the formation of Botrytis only in certain vintages and the wines cannot be produced in every year.