The grapes withering to obtain the MUFii is achieved by a physical phenomenon, a dehydration through ventilation and a biochemical process, that is the formation of “noble rot”.
The “noble rot” is a consequence of the grape invasion by a microscopic fungus that develops only in particular and favourable climate conditions: Botrytis Cinerea.
This is in fact the name by which we generally identify a particular kind of mould that allows the creation of mouldy or “botrytized” wines.
Obviously, not every rot makes such a good action on the grapes and not all the grape types are suitable to be affected by this particular mould, not even all the territories are appropriate to grow the “noble rot”.
The noble rot formation is therefore a peculiar combination of many factors, morning moisture, windy climate during the day and a temperature range between day and night.
The grapes withering is also related to an adequate type of grape, to the strenght of the peel and to the protection layer of bloom (the waxy substance protecting the grape surface), that are characteristics typical of each variety.
The bunches must not be damaged by any natural or mechanical touch.
The vintage volume decrease, caused by the noble rot, may reach a 40-50%, but this never gives a sugar and organic acid consumption. The quality is obtained, therefore, to the detriment of the yield that is subject to a great reduction.
The withering result and the Botrytis Cinerea process is different every year.
A continuous and excessive humidity may develop another type of mould taking to opposite effects: the grey rot or ignoble rot, a factor that ruins irreparably the grapes making them unusable for the wine production.