What is the noble rot fungus?

The noble rot fungus is Botrytis cinerea, a specific type of grey fungus renowned for its beneficial effects on wine grapes, leading to the production of highly prized sweet wines.

This unique phenomenon, often referred to as "noble rot," is a controlled form of fungal infection that dehydrates grapes while concentrating their sugars, acids, and flavors. Unlike its more common destructive form, where Botrytis cinerea causes grey mold and spoilage, noble rot occurs only under precise environmental conditions.

Understanding Botrytis cinerea and Noble Rot

While Botrytis cinerea is widely known as a destructive plant pathogen, it acts as a "noble rot" when the conditions are just right. This transformation from a harmful mold to a winemaking asset is crucial for producing world-class dessert wines.

• Fungus Type: Botrytis cinerea is a necrotrophic fungus, meaning it kills the host cells to obtain nutrients. However, in the context of noble rot, its action is carefully managed by specific weather patterns.
• Appearance: The fungus itself is typically grey, and when it affects grapes, it can give them a shriveled, dusty appearance.
• Impact on Grapes: The fungus pierces the grape skins, allowing water to evaporate through the microscopic holes. This process, essential for noble rot, concentrates the grape's internal components, resulting in intensified sweetness, richer flavors, and a distinct aromatic profile.

Ideal Conditions for Noble Rot Development

The delicate balance required for Botrytis cinerea to manifest as noble rot is why noble rot wines are so rare and geographically specific. The fungus thrives and performs its beneficial action under very particular climatic conditions:

• Temperature: Typically requires warm conditions, ideally around 20 degrees Celsius.
• Humidity: Needs high humidity, usually above 80%, for the initial infection to take hold and for the fungus to develop properly. This is often provided by morning mists or fog.
• Alternating Conditions: Crucially, these humid periods must be followed by dry, sunny, and windy conditions. This alternation allows the grapes to dry out and prevents the fungus from turning into destructive grey mold.

International Names for Noble Rot

The significance of noble rot in winemaking is reflected in the various names it has acquired across different wine-producing regions:

These terms highlight the global recognition and importance of this unique fungal interaction in viticulture. For more in-depth information, you can explore the Noble Rot phenomenon.