Final answer:
Wines can be fortified during or after fermentation. During fermentation, the addition of a fortifying agent like brandy increases alcohol content and stops fermentation early, resulting in a sweeter wine. Post-fermentation fortification increases alcohol content without altering sweetness.
Step-by-step explanation:
Wines can be fortified at two different stages of the winemaking process. The first opportunity to fortify wine is during fermentation, when yeast converts the sugars from grapes into alcohol. At this stage, fortifying agents such as brandy can be added to the wine, which will increase the alcohol content and halt fermentation. This creates a sweeter, stronger wine because residual sugar that has not been converted into alcohol remains in the wine.
The second chance to fortify wine is after fermentation has been completed. This is when the fermentation process no longer produces alcohol, and adding a fortifying agent at this point will raise the alcohol level without affecting the wine's sweetness. The choice of when to fortify the wine depends on the desired flavor profile and characteristics of the finished product. Wines like Port are fortified during fermentation, while others might be fortified post-fermentation.