Dried grapes From the vine to the mat: how grapes are dried This is the last stage of the vine's cycle before its winter rest. It is called overmaturation. The grapes lose water and the sugars are concentrated and the acidity diminishes. However, it is risky to leave the grapes on the vine, exposed to bad weather, so the grapes are picked (late if the weather allows it) and placed to dry in special airy rooms, with the grapes hanging from the ceiling or laid out on mats or trelliswork. Sometimes the grapes are laid on tables covered with straw. This allows air to get to the grapes easily and hence the term used by the French for dried grape wines: vins de paille. The grapes stay like this for several months, sometimes until February or March and lose weight (from 100kg of grapes the figure may fall to 60 kg or sometimes even less). This gives a must with very high sugar levels destined to produce dried grape wines. Fermentation usually last for many months and is very slow. The wine is aged in small wooden barrels. These wines have a high alcohol level and are aged for two or three years before being sold.