Botrytis Cinerea

Definition - What does Botrytis Cinerea mean?

Botrytis cinerea is a necrotrophic fungus that affects many plant species. It is well known for its effects on wine grapes. There are three types of infections on grapes that could develop from Botrytis cenerea:

  1. Grey Rot - caused by wet or humid conditions, this rot results in lost bunches and has no positive applications in winemaking
  2. Bunch Rot - caused by a wound on the grape allowing the whole bunch to be completely infected by the fungus.
  3. Noble Rot - the form of the fungus that winemakers use, this is caused by a wet period followed by a dry period.
Noble rot is when the fungus covers the skins of the grape, sucking the water from the berries and concentrating the sugars, fruit acids and minerals. The results are a sweet, concentrated wine.

WineFrog explains Botrytis Cinerea

As with many of winemaking tools, Botrytis cinerea requires specific conditions in order to properly affect the end wine. Temperature and humidity are two critical factors. The temperature must be between 20 - 25°C. Humidity should start at 85 - 95%. After 24 hours at that level, humidity needs to drop to 60% in order for the fungus development to slow appropriately.

Under these ideal conditions, the mold penetrates the grape skins. The skins become permeable but they don’t split (splitting would cause a wound which could lead to bunch rot). The fungus dries out the berries, concentrating the sugar; as the water dries up, so does the "food" the fungus eats, which slows the development. Eventually the fungus stops reproducing.

When the process is complete, the grape’s composition has changed. Though the fungus consumes 35 - 45% of the sugar found in the berry, the concentrated juices that remain are very sweet. Organic acids - tartaric and malic - are limited, which means acidity is low. Glucomic acid and glycerol are formed. The other issue is that it can cause filtration problems and inhibit alcoholic fermentation; in fact, red wines might not survive the process without careful monitoring.

Botrytis cinerea is used to make several different types of dessert wines across the world:

  • France
    • Monbazillac
    • Coteaux du Layon
    • Sauternes
    • Sélection de Grains Nobel
  • Germany & Austria
    • Beerenauslese
    • Trockenbeerenauslese
    • Ausbruch (Austria only)
  • Hungary & Slovakia
    • Tokaji
  • South Africa
    • Noble Late Harvest
  • Romania
    • Grasa de Cotnari
These wines and others made with Botrytis cinerea infected grapes have an aroma of honey suckle and a bitter finish on the palate. As with Late Harvest and other sweet wines, Botrytis cinerea wines should be paired with any naturally sweet dessert.