Manufacture of Fortified Wines:

Some famous wines are classified as fortified wines because their alcohol content has been strengthened, or fortified, by adding a high alcohol spirit to the wine. The most illustrious examples of such wines are Porto, or Port, from Portugal, and ]erez, or Sherry, from southern Spain. It has often been claimed that the original reason for fortifying wines was to stabilize and preserve the wines, since alcohol is both a preservative and stabilizer. There is some truth in this claim, evidenced by the fact that both Porto and Sherry were largely developed by British merchants, who shipped the wine fairly long distances, as they built the British wine trade. It is also true that in Andalucia (Andalusia), where Sherry is produced, the local inhabitants and winery workers drink a lower alcohol version of Sherry than that which is exported. Perhaps the most important factor in discussing fortified wines, however, is that it is generally agreed that the table wines from these fortified wine areas are not particularly good.

Whatever the reason, fortification of a wine means simply that a high alcohol spirit, usually a lacally made brandy or eau de vie, is added to the wine during or after fermentation. The difference between adding the spirit during or after fermentation is the difference between a dry and a sweet fortified wine.

If the spirit is added during fermentation, as is the case in Porto, the addition of the spirit will raise the alcohol level of the fermenting wine to a level at which fermentation will stop-beyond 14.5 percent alcohol. However, not all of the original grape sugars will have been converted to alcohol, leaving residual sugar in the now-sweet fortified wine. If the spirit is added after fermentation, as is the case in Sherry production, the original grape sugars in the grape juice are all converted to alcohol, producing a dry wine. When the spirit is added to this wine, it becomes a fortified wine. (In the case of Sherry, producers have the option of sweetening the Sherry at a later stage.