I often get questions regarding the somewhat misunderstood production method involving drying some or all of the grapes before making wine, so I thought I would create a simple explanation of this process.
There are a number of wines that are produced using methods of drying grapes prior to crushing/fermentation. These wines are (according to the Oxford Companion to Wine) all classified as "Dried Grape Wines".
The idea is to partially dry the grapes (whole berries) so that the flavors and sugar content is concentrated, increasing the intensity of both in the final wine. These are techniques that were historically practiced in order to enhance the preservation of the wines over time. Higher sugar levels and/or alcohol levels with extend the life span of a wine - especially if that wine is to be moved/sold outside its local area of production.
There are examples of these wines throughout Italy: Passito, Vin Santo, Vino Santo, Amarone and Recioto. But I have also observed this technique in farther corners of the wine world: David de Trafford makes his Straw Wine in Stellenbosch from grapes that been allowed to partially dry in the sun, for example.
This picture (taken in Trentino in 1998) is of racks of grapes drying in preparation for Vino Santo.
The concept is simple enough; healthy, whole, ripe grapes are placed on wire racks, straw matts or some other surface with plenty of air circulation (it is important for the grapes to stay dry in order to prevent rot) either outside or in specially designed rooms. These grapes are then left anywhere from several weeks up to several months depending on the wine being produced. The sunlight or warm dry air will help to facilitate the drying process. Grapes are usually checked periodically and any rot is removed. Once the desired concentration is achieved the grapes are pressed and fermented.
Generally speaking the outcome will be a sweet wine with substantial concentration of flavors. The desired style or local custom will then dictate the winemaking. Many of these wines will benefit from some sort of wood aging. This creates added complexity to the wines.
Some of my favorite examples of these wines are:
Falchini Vin Santo - San Gimignano, Tuscany
De Trafford Straw Wine - S. Africa
Bertani Amarone - Veneto, Italy
At Falchini Vineyards in Tuscany they have two Vinsantarias, or cellars for aging the Vin Santo. One cellar is a traditional, underground cellar and the other is essentially an attic cellar. They also use five different types of wood to age their Vin Santo. The result is one of the most complex and pleasing wines I have had the pleasure of drinking. There are literally hundreds of producers of these wines, though.