🍷 Noble rot

Noble rot is a special, beneficial form of grape infection by the fungus Botrytis cinerea. The same fungus usually does harm and causes grey rot, but in rare conditions its action becomes welcome: overripe berries dry out and the juice in them concentrates several times over.

Weather decides everything. Damp nights and foggy mornings let the fungus take hold, while dry, sunny days keep it from developing into the harmful form. Heavy rain and high humidity, by contrast, lead to grey rot. The fungus makes the skin permeable, water evaporates and the berry shrivels; the infection lasts about 10–20 days, and the high sugar eventually stops the fungus itself.

The figures are striking. In Sauternes the juice of such berries usually holds about 350 g of sugar per litre, and in Tokaj up to 700 g/L. The fungus produces glycerol: more than 7 g/L, and in aszú berries and those for Trockenbeerenauslese up to 30 g/L. Wines from these grapes smell of peach, apricot, quince, honey and caramel.

The oldest style is Tokaji aszú, followed by German Beerenauslese and Trockenbeerenauslese and French Sauternes. In the Romanian appellation Cotnari, the rules explicitly mention sweet wines that come about in a long, dry autumn under the action of noble rot.

Why it matters to you. Noble rot does not happen every year, and the affected berries are picked selectively, sometimes one by one. Do not confuse it with grey rot: the fungus is the same, the result is the opposite. Sweet wines are best enjoyed in small servings.