Noble rot (Botyritis cinerea as it is known technically) or ‘Pourriture Noble’ (in French) is a special set of fungal conditions experienced by white wine grapes when they become infected by grey rot fungus as the grapes approach their maturity. When picked, pressed and the juice fermented, the resultant so-called “botyrised” wines have a distinctive sweeter taste and flavour.
Grey rot is a universal fungal disease that attacks many fruits as they start to ripen. The process of noble rot in white wine grapes is brought on by a mixture of cool humid conditions, such as rain or overnight fog, followed by warmer dry daytime weather. As the rot takes hold, it penetrates the skins of the grapes and starts to feed on the contents inside reducing water and acidity. This causes the grape to shrivel up and the remaining juice to sweeten and concentrate its flavours.
Grape bunches are infected by noble rot at different rates. This means that, if you want to pick the grape bunches at the optimum point of ripening, the harvesting has to be carried out multiple times by hand. The best producers may pass through the vineyard to cut and collect the fruit five or more times. Each pass / harvest of the vines is called a ‘trie’ in French.
Although grey rot is a worldwide fruit fungal disease, noble rot only occurs in a few places where the specific climactic conditions exist and white wine grapes are grown. The best-known regions for production of these “sweet white” wines are Sauternes / Barsac in Bordeaux and Tokaj in Hungary.
Noble Rot is nature’s way of making beautiful sweet white wine.