This issue depicts various stages of the Port wine production, including the transport by rabelo boats down the Douro river to the cellars in Vila Nova de Gaia, where the wine ages. Vines have been planted in the Douro valley for over 2000 years. The export to England started in the late 17th century and it soon became very popular, mainly due to two factors: the war with France deprived England from French wine, and the Methuen Treaty of 1703 allowed English merchants to import Port wine at a low duty. To avoid it becoming spoiled during its shipment to England, Port wine was fortified through the addition of aguardente. In 1756, the Douro valley region was demarcated and the wine production was regulated, making Port wine the world’s oldest regulated appellation.
If you want to try your hand at making Port wine, I heartily recommend Vintage, a very good board game that simulates in a simplified way all stages of production, from planting the right types of grape to selling the wine, while managing the stock of aguardente and the available capacity in the cellars and boats. The best manager, who sells the most wine at the best quality, wins the game. I should say I participated in the production of Vintage by translating the rules into English, but I have no commercial interest in the game.
The stamps were designed by Cândido da Costa Pinto, lithographed by the Mint on glazed paper sheets of 5×10 stamps with perforation 13¾, and circulated from 30 December 1970 to 31 December 1983.