Still wines, red and white, generally attain a natural alcohol level of between 8.5 and 15 per cent after standard fermentation. To make a fortified wine, grape spirit is added at different stages of the fermentation process depending on the style required. The addition of this alcohol has the effect of killing off the yeast and arresting the fermentation while at the same time boosting the alcohol level usually from 17 to 24 per cent.Sherry and Port are perhaps the best known household names in fortified wines - so why are they so different? Apart from location, grape varieties, soil etc. there is a fundamental difference in the way they are vinified. With Port, the alcohol is added during fermentation, thus halting the process and leaving some residual sugars unconverted. Sherry, on the other hand, is always fermented fully to dry with the alcohol added at the end of the process - any sweetening is performed subsequently.
The VDNs of France such as Muscat Beaume de Venise, Banyuls etc have grape spirit added at different times depending on the style required but always retaining that natural sweetness and high alcohol content. In certain cases spirit is added to grape juice before fermentation - Pineau des Charentes from the Cognac region has young Cognac added in this manner and then aged in cask.
