Raisin wine vinification
Made from grapes that have undergone natural or forced dehydration processes, raisin wines are considered special wines. However, from a regulatory point of view, they are to all intents and purposes 'normal' wines: once vinification has been completed, before marketing, they do not undergo any other technical interventions and do not have any special flavourings/components added.
Made from white or red grapes, raisin wines are perfect meditation and dessert wines (but can also be paired with mature or blue cheeses). The most illustrious examples of Italian dessert wines are Amarone della Valpolicella, Sforzato di Valtellina, Passito di Pantelleria, Sagrantino Montefalco and Moscato di Scanzo. All are characterised by the drying of the grapes before vinification.
Grape drying techniques
The drying of grapes is an ancient technique that was used thousands of years ago to preserve the grapes for longer. However, in order for them to be dried, the grapes must come from vines with a high acid content and must have a very resistant skin: otherwise mould could form (wines made from very late harvested grapes, on which the so-called 'noble rot' forms, are known as 'mildew wines').
The drying of the grapes can take place on the vine or after the harvest.
In the first case, known as on-vine drying, the grapes are left to over-ripen on the vine and are therefore harvested 10-30 days after the deadline, according to the late harvest technique.
In the second case, the grapes are dried after harvest either naturally or by force. Natural drying consists of a slow dehydration of the grapes which, once harvested, are left to air-dry in a place that depends on the zone in which one is located (in the sun in southern Italy, on attics or protected lofts further north): placed diagonally on metal nets or large mats, or hung vertically, the grapes gradually dehydrate. Forced raisining, another off-vine raisining technique, involves placing the grapes in fruit lofts (specially ventilated rooms), with ventilation at 30°C and humidity at 55-60%. While natural drying lasts about 80 days, forced drying lasts only about ten.
A second method of on-vine drying is the twisting of the bunch stalk, which is broken but not completely detached from the vine: the berries, which no longer receive nutrition, are thus left to dry in the heat and sun. The third way in which grapes are dried on the vine is through the attachment of the berries by 'noble rot' (Botrytis Cinerea): under special climatic conditions, ripe berries are infected by the fungus, their skins become porous and water evaporates. The berries affected by noble rot are harvested one by one, to produce so-called 'botrytised wines'.
Compared to off-vine dried wines, on-vine dried wines are sweeter. This is because, in the course of over-ripening, the berries continue to be nourished by the plant: this 'bond' in fact opposes dehydration by supplying the berries with certain nutrients, starting with sugars.
Fermentation of dessert wines
Once the grapes have dried, they are crushed and then destemmed to remove the stems from what will become must. Only then will fermentation take place, and thus the progressive transformation of the sugars into alcohol. This is the phase that precedes ageing and bottling.
Since the must obtained from the dried grapes is very rich in sugar, its fermentation is extremely slow. There are cases where it does not even take place or, if it does, produces wines with a very low alcohol content. When fermentation is complete (by lowering the temperature, adding sulphur dioxide or filtering), the wine is matured in wooden barrels and - finally - bottled.
Raisin wines and liqueur wines, the differences
Often confused, dessert wines and liqueur wines are actually quite different:
- Raisin wines are natural wines produced by traditional vinification, except for the drying of the grapes. This step allows the grapes to reach a sugar content of 30-40%.
- Liqueur wines, on the other hand, are made from aromatic grapes. The fermentation of the must is interrupted by the addition of alcohol or spirits, and the result is a wine with an alcohol content of between 15° and 22°. They are therefore wines with a higher total alcoholic strength than traditional wines, but equal to (at most) twice the strength of the wine from which they derive.
Some liqueur wines are made from dried grapes, to whose must, however, alcohol or wine spirits are always added.