Managing Botrytis-infected fruit, must and wine

Botrytis cinerea is a weather-driven fungus which causes the grapevine diseases botrytis bunch rot and grey mould. High humidity or prolonged rain in conjunction with cool or mild temperatures results in persistent moisture on berry surfaces and promotes infection and disease development. Previously infected sites and sheltered vineyard areas such as hollows are at greatest risk of developing the disease.

Monitoring, symptoms and control in the vineyard
The following fact sheets provide detailed information about managing Botrytis in the vineyard:

Implications in winemaking
Botrytis can cause problems during winemaking. It produces an oxidative enzyme called laccase which in the presence of oxygen can cause oxidative spoilage and rapid browning of must. Laccase activity is the main marker for Botrytis infection, and can be analysed both qualitatively and quantitatively. Preventing this enzyme from causing damage requires techniques that minimise or eliminate exposure to oxygen.

Botrytis can oxidise glucose to produce gluconic acid. As gluconic acid is not utilised by yeast or bacteria it is sometimes used as an indicator of infection. Botrytis can also produce glycerol and, together with bacteria, can produce high levels of acetic and lactic acid.

Botrytis growth can result in formation of polysaccharides that can create clarification problems in juice and filtration problems in wine. The alcohol precipitation test for polysaccharides can be used to determine if this is causing clarification or filtration issues.

The presence of Botrytis on grapes can also lead to the presence of a mouldy character in wine.

Eliminating or minimising the quantity of Botrytis-affected fruit processed will reduce the potential effects of oxidative damage; however, a holistic approach is required that involves many aspects of the winemaking process.

Dealing with Botrytis infection in red grapes requires different treatments from those used with white grapes. The Managing Botrytis-infected fruit fact sheet sets out processing strategies for red and white winemaking that can help reduce the risk of oxidative damage from Botrytis-infected fruit.

For additional information, refer to the Information pack on Botrytis, which allows online ordering of articles and other resources.