Botrytis cinerea is a type of mold that occurs on the outer skins of grapes late near harvest time, if climate and humidity conditions are just right.
Botrytis cinerea is also referred to as “noble rot”, and causes grapes to lose water, increasing the concentration of their natural sugars. While most molds and pests could damage a wine crop, Botrytis has the opposite effect. It is desired and hoped for by winemakers who would like to produce sweet, dessert-style wines.
It is through the presence of Botrytis that that many sweet, late harvest wines are produced.