Fortified wines were born of the need to protect wines on long sea voyages. During the sixteenth and seventeenth centuries, trade expanded to encompass the globe. Unfortunately, many wines from Europe became spoiled on their long journey across the ocean to the colonies. To counteract this problem, someone hit on the bright idea of adding brandy to the wine to stabilize it. These new fortified wines were then better able to withstand the rigours of a long journey in the hold of a ship and the fluctuating temperatures they would encounter on the sea and in the tropics. Once the fortified wines reached their destination, they were often preferred to regular wine because of their higher alcohol content (woo hoo!) and robust flavour.
Fortified wines generally contain between 17 and 21% alcohol. As a result, they are more stable than ordinary table wines and less likely to spoil once they have been opened. Well-known fortified wines are sherry, port, Madeira, and Marsala.