The Latin name for the fungus or mould that, given certain conditions, attacks certain grapes in certain regions.
In France it is called pourriture noble, in Germany edelftiule, in Italy muff a nobile. In England it is usually referred to as ‘noble rot’, to differentiate it from the more usual type of grey rot that also attacks grapes to their detriment. Botrytis attacks grapes when outside conditions tend to be both warm and somewhat foggy, as can occur late in a vintage season. The grapes shrink, the skin contracting and resembling old, shrivelled suede, the juice inside each grape is concentrated, becoming intensely sweet, while the outside of each grape developes a fuzzy mould as on withered raisins quite dried up. If you taste a grape like this, it will, literally, melt in the mouth! Because the noble rot has to be allowed time to develop and affect the grapes, considerable risks are involved by leaving them on the vines.
Sometimes, vineyard owners prefer to pick the grapes while the weather remains good and simply put all of them into the vat for fermentation. If the noble rot grapes are to be picked, they have to be selected, usually one by one, in good years by small bunches, very seldom by the whole bunch, as Botrytis does not attack all the grapes in a bunch at the same time and at the same rate. This means that pickers have to be experienced in knowing exactly when a particular grape should be picked and, also, that the teams of workers often have to pass through a vineyard many times, picking a few grapes from each bunch at a time. All this makes for an expensive wine at the end. However, the greatest sweet wines are made in this way, in the Quart de Chaume region of the Loire, some in Monbazillac, as well as in Germany (the trockenbeeren and beerenauslesen wines) and some late harvested wines of South Africa, in addition to the Sauternes.
Some interesting experiments have been made in certain U.S. vineyards, where the Botrytis has been artificially induced, so as to act on fully ripe grapes; but it seems that, to date, this is still not wholly satisfactory. As in South Africa, many of the U.S. vineyards have climates that are dry rather than humid; unlike those of the Gironde, Rhine, Mosel and Loire, where early autumn mists encourage the action of the fungus.