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Vinification of sweet
wines and special wines
Before the alcoholic
fermentation must is essentially sugary
water. The action of the yeasts changes these sugars
into alcohol. In order to obtain sweet wines all that is required is to limit
this process. The most commonly used technique is to interrupt the fermentation
when the desired alcohol level has been reached, filter the must using filters
with a very fine mesh to trap the yeasts, then allow it to continue. The operation
is repeated several times and becomes weaker and slower.
For dried grape wines
the grapes are dried, either naturally or artificially, thereby increasing their
sugar level through evaporation of water.
Once they have reached the required
degree of dryness the grapes are vinified as for white wine, with a fairly slow
fermentation at low temperatures so as not to cause the aromas to alter. The wine
will also have to remain quite a long time in the cellar in order to refine its
character. These types of wine may be considered mature after three to four years.
One of the most famous examples is the Tuscan Vin Santo, which is made from the
best bunches of grapes. These are allowed to dry on mats or trelliswork, generally
in attics which are well aired all year round. The long maturation takes at least
three years in small barrels (caratelli).
Red Muscat (a sweet red wine from
the Trentino and Friuli areas) is, however, left to overripen on the vine. The
alcoholic fermentation takes place in small vessels and, after the malolactic
fermentation, the young wine is sweetened with concentrated must in order
to bring it to a strength of 15-16°. The wine is then left to age in small barrels
for 2-3 years.
The so-called botrytized wines are another matter again: these
are obtained from grapes attacked by Botrytis
cynerea or 'noble rot'. This mould causes changes inside the grape which alter
the grape's metabolism, causing a substantial increase in aromatic substances.
In certain cases for these wines it is possible to add ethyl alcohol or concentrated
must in order to increase the alcoholic
strength. The vinification is similar to the process used for dried grape
wines.
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