Licensed to Kill: A Look at Noble Rot

Jackson, Ron. Wine Science Principles and Applications Plate 9.1 - Cluster of grapes at different stages of rot.

Jackson, Ron. Wine Science Principles and Applications Plate 9.1 – Cluster of grapes at different stages of rot.

The fungus Botrytis cinerea — a type of gray mold — is the kind that grows on the old berries in your fridge, but in the vineyards of Europe (and more recently some other wine-producing regions artificially infected, but more on that later) B. cinerea doesn’t always turn valuable fruit into a furry mush. Also known as noble rot, B. cinerea has the potential to positively change wine grapes, in the right conditions. Depending on a vineyard’s microclimate, infection can result in either gray rot, which essentially ruins the grapes, or noble rot, which leads to unique dessert wines such as the Tokaji Aszú of Hungary, the higher Prädikat wines of Germany, and the Sauternes of France (the most prized of which can fetch $750 a bottle!).

In a single vineyard there can be completely healthy grapes, grapes with gray rot, and grapes with noble rot, all in close proximity to each other. The required conditions for noble rot formation are incredibly narrow. Like with most fungi, humid conditions favor formation. However, alternating dry and rainy periods, particularly frequent morning fogs, are necessary for the formation of asexual conidia (spores). Therefore, noble rot seldom occurs in hot and dry areas, since sunny and windy conditions allow more water evaporation. Continue reading