Any fruit or vegetable is, under the wrong conditions, subject to rot, often in the form of an infection from Botrytis cinerea. The fungus is found from the tundra to the tropics, thriving in areas with ample humidity – at least 80 percent – and temperatures between 12 and 25 degrees Celsius. Most farmers view it as a pathogen, but winegrowers, in the right conditions, see it as pure gold. Sauternes, Tokaji, and other botrytis-affected wines are among the world’s most treasured libations, and science is just beginning to understand how botrytis creates these luscious wines, which have earned the fungi the nickname “noble rot.”
Noble rot, as opposed to undesirable bunch rot or gray rot, only occurs under specific conditions. “For producing botrytis, the east side of the Neusiedlersee was always better than the western side,” says Gerhard Kracher, the third-generation owner of Weinlaubenhof Kracher in Austria, who produces a range of wines that rely on botrytised grapes. Lake Neusiedl, the largest natural lake in Central Europe, and numerous smaller lakes nearby provide moisture. “There’s always fog in the morning hours,” says Kracher, “but there is always some wind coming in during the day, blowing out the fog. So it’s the combination of wetness and then dryness, with the sunshine coming through, that’s the perfect climate for botrytis to grow.”
The fine line between beneficial noble rot and devastating gray rot has prompted researchers to investigate how the noble version occurs, how exactly it affects the grapes, and how it contributes to such captivating finished wines.
How grapes respond to botrytis
According to Dario Cantù, Ph.D, a professor of viticulture and enology at UC Davis, the wet-to-dry conditions that Kracher describes give the grapes a chance to resist the invading fungus.
In 2015, Dr. Cantù conducted a study in partnership with Dolce, Far Niente’s Napa Valley project focused on noble rot wines. “What we saw is that the slowing down of the infection during the day allowed the fruit to respond, metabolically, to the infection. This is very different from what happens with bunch rot, where the infection goes so fast that the plants don’t have a chance to readjust their metabolism.”
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