Botrytis or 'Noble Rot' is a type of fungus that shrivels and decays wine grapes.
It requires very specific conditions in the vineyard if it is to be a boon, rather than a bane. Cool humid mornings are ideal, as they allow for moisture to collect on the grapes so that the fungus can grow and pieces the skins. Sunny afternoons with gentle breezes should then follow so that the fungus growth is slowed down and the grapes have a chance to dry out.
As the grapes slowly dehydrate on the vine, the sugar levels intensify and the resulting wines can be more viscous and alcoholic. Although the most famous examples of wines with botrytis are sweet, there are off dry and dry examples too, where the winemakers use botrytis to build complexity and texture.
The botrytis also gives certain characteristics to the finished wine. Common descriptors are honey, marmalade, dried apricot or mango and ginger. Because botrytis compromises the integrity of the skins, wines made from these grapes are often more phenolic, as tannins from the skins bleed into the juice more easily when pressed. This is but one element that gives these wines such longevity.
Some of the most famous examples of wine with botrytis are Tokaji, Sauternes, Quartes de Chaume and the Auslese, Beerenauslese and Trockenbeerenauslese wines of Germany.