The origins of the Port trade began in the 17th century, when wars with France deprived the British and Dutch of French wines. Both ventured up the rugged Douro River Valley for wines, but it wasn't until the mid-18th century, when brandy was added to the traditional wines of the region to stabilize them for their journey across the seas, that modern Port began to take form. Port today is a sweet fortified wine that is high in alcohol due to the addition of a neutral spirit during fermentation. The fortification stops fermentation by killing the active yeasts while leaving some of the unfermented sugars. The level of sweetness varies according to the shipper's house style, but the alcohol level is generally about 20 percent.
Port is made all over the world, including America, Australia and South Africa.
However, true Port is made in northern Portugal from grapes grown in the upper Douro Valley, about 100 miles east of the town of Oporto. Traditionally the grapes are harvested in the Douro and made into Port there, but the maturation is done in warehouses in the town of Vila Nova de Gaia, just across the Douro River from Porto. Firms such as Taylor Fladgate, Fonseca and Graham all have facilities in Gaia. Port cannot be compared to any other wine in the world. The Douro is one of the most difficult wine-producing regions in the world.