(n.) A sweet fortified wine from the Douro Valley of Portugal invented in the 17th century to preserve wines traveling to England by ship. Port is made by adding grape brandy to wine during fermentation process. The high alcohol of the brandy kills the yeast, which had been converting sugar to alcohol, leaving a residual sweetness and gaining a higher alcohol content from the brandy, both signatures that help to preserve the wine.
There are numerous classifications for port, largely having to do with aging rules. Vintage port, prized among wine collectors, is only made during the best years and is aged for two years in oak casks before bottling with little exposure to oxidation. With a deep red color and fruity flavor, it is meant for aging in bottle for many years and often commands a hefty price tag. Tawny port is made from a blend of vintages that have been aged in oak casks between 10 and 40 years. During the aging process, it gains some exposure to oxygen, which lends it a nutty flavor and brownish-red color. Colheita port is a tawny port made from a single vintage and aged for at least seven years. Ruby port is the youngest and the most simple, made from a blend of vintages aged two or more years in stainless steel or neutral oak casks, and meant to be drunk young.
While Port is largely anchored in the wine world, it has a long history in cocktails as well, used frequently as an ingredient in historic punches such as the St. Charles Punch or the Port Wine Sangaree. When using it in mixed drinks, ruby port is your best choice.