Regular wine has an A.B.V. ranging from 7% to 13%, while spirits are much stronger, running from 40% to as much as 90%. Adding spirits to wine gets you to a point in the middle, giving fortified wines an average A.B.V. of around 17% to 20%. There’s an obvious appeal here to certain people, but the practice of fortifying wine actually arose from practicality.
Prior to the advent of fridges, shipping wine long distances — particularly overseas — was an absolute nightmare. Wine casks are not airtight, and with enough exposure to air, wine will eventually become vinegary as it oxidizes. Since alcohol itself won’t expire, increasing the alcohol content of the barrels can keep them from spoiling, and this was the initial motivation for adding spirits to wine.
Fortifying wine also has a profound effect on its flavor, depending on the wine and spirits used as well as the manufacturing process. Fortified wines tend to be sweeter than regular ones. This is because, during the winemaking process, the natural sugars in grapes are gradually converted into alcohol; however, spirits are added to the mix before the wine is done fermenting, leaving the drink in a sweeter state.
Fortified wine may also have herbs, spices, or other ingredients added for flavor, which would make it an aromatized wine. Today, different types of fortified wine are subject to regulations on A.B.V., the aging process, other additives, and the kinds of wine and spirit involved.