Fortified means that extra alcohol has been added to a wine. In the beginning it was done to preserve the wine for shipping, but fortified wines have become specialties to be enjoyed on their own terms.
If you were making regular table wine, you would crush the grapes and let fermentation take its course. You would end up with a dry wine with about 12 percent alcohol. For a fortified wine you would add a brandy (usually made from the same grape as the wine) or a neutral spirit.
If you add the brandy after fermentation, the fortified wine is dry, with no residual sugar. If it is added before fermentation is complete — before all the natural fruit sugar is consumed — the alcohol stops the yeast from converting the sugars, and you have a sweet fortified wine.
There are four primary types of fortified wines: port, sherry, Madeira, and Marsala. The popular drinking wines are port and sherry. Madeira and Marsala are better known as cooking wines, but there are good bottles of each for drinking. Here is a quick look at each:
Port is sweet and is most often served after a meal. True port comes from the Douro Valley in Portugal.
Sherry, from the vineyards of southern Spain, can range from dry to sweet. Pale, dry sherry is served chilled as an apéritif. Darker, sweet sherry is usually enjoyed as an after-dinner drink.
Madeira is named after its birthplace, a Portuguese island off the coast of Africa. Unlike other fortified wines, Madeira is heated in its production. It can be sweet or dry.
Marsala, named for the town on the western tip of Sicily, comes both dry and sweet. Of all the fortified wines, Marsala is the least distinctive as a beverage and is mostly used for cooking.