Botrytis Cinerea is a fungus which affects many plants. It affects grapes in one of two ways. The first, grey rot, results in the loss of the affected bunches and so is a bad thing. However, the second, noble rot, helps concentrate the flavours of the grape and sugar levels which allows winemakers to create wines that are sweet, concentrated in flavour and with quite distinctive flavours and aromas along the lines of dried apricots and orange marmalade.
The sugar levels are concentrated as the fungus makes the grape skin more permeable to water, thus allowing water to evaporate from the grape. In order for this to happen, the grapes require damp morning conditions but warm, sunny afternoons. If the environment is too damp then it is considered grey rot.
