What Is Noble Rot? Botrytis Cinerea: A Welcome Infestation

Sweet wines have a sick secret. Believe it or not, a grey fungus known as Botrytis cinerea is largely responsible for the unique flavor of many famous dessert wines. Heck, winemakers love Botrytis so much that they’ve described it as the “Noble Rot.”

So, how could a fungus related to athlete’s foot possibly improve the taste of wine? The quick answer is that Botrytis effectively traps the sugar in grapes as they become dehydrated. When winemakers press these “rotten” grapes, they are rewarded with higher-than-average sugar and alcohol contents.

In addition to heightening the sweetness factor, Botrytis produces a chemical called phenylacetaldehyde. This aromatic compound adds great complexity to a wine’s aroma. Although it’s hard to pin down, many wine enthusiasts liken the scent of phenylacetaldehyde to honey or caramel. Phenylacetaldehyde also has rich floral notes and could be found in roses and buckwheat.

It’s most common for the Botrytis fungus to form on ripe grapes that are grown in damp areas. To help encourage this fungus, vineyard owners will often plant some of their crop close to rivers. Winemakers could also use frozen Botrytis-infested grapes to produce many unique flavors.

Since Botrytis is so closely associated with sweetness, it shouldn’t come as a surprise that most dessert wines are made from these grapes. Typically, people enjoy these sweet wines with equally sweet snacks such as fresh fruit, but they could also be served during a main course.

Although nobody’s sure about the origins of the Botrytisation process, Hungary has a very long history of using Botrytised grapes. One of the most commonly Botrytised grapes in this region is known as Furmin, but other popular Hungarian strains include Zéta and Kabar.

In France, prominent grape varieties that often go through this “rotting” process include Sémillon, Muscadelle, and Sauvignon blanc. In Northern Europe, some winemakers encourage Botrytis on Riesling grapes. You could usually tell which Riesling wines used Botrytised grapes because they are set at a significantly higher price tag. A few other grapes you might’ve heard of that are good for attracting Botrytis include Chardonnay, Ortega and Scheurebe.

Now go ahead and try a sweet wine!