There are five key grapes used for the majority of Port types: Touriga Nacional, Touriga Franca, Tinta Roriz, Tinta Barroca and Tinto Cão. Of course there are many other grapes that can be added to the blend and each grape adds a unique component to the final assemblage. Some add aromatic charm, others body weight, complexity and richness, still other grapes bring a unique flavor profile to the party, but all have their place and raison d’être.
There are nearly 80 (white and red) grape varieties found in different blends of Ports, but the grapes used must be from a specific list that was approved by the Portuguese Government in 1940. Up until the past two decades, most winemakers and master blenders had no idea which grapes were used in their Vintage Ports. Even many vineyard owners and their vineyard managers were mostly clueless about which grapes were growing on their property. Until the late 1980s, most vineyards were a cluster of "field blends" with plantings of varying grape types mixed together. That is one of the positive changes that have occurred in recent times. Recent plantings and just about all that have taken place in the past two dozen years, segregate grape types, called “block planting.”
After the grapes are picked, they are either trodden by foot in stone tanks (called a Lagar), or placed in large stainless steel tanks where they are crushed by mechanical means. They are then left in the tank or lagar for 1-4 days during the fermentation process in which the naturally occurring sugars are converted to alcohol. During fermentation, when about half of the sugar is turned to alcohol, Aguardente (brandy) is added to prematurely stop fermentation by killing the yeast cells. This also raises the alcohol content to about 19-21% alcohol by volume (ABV) and leaves a good deal of residual sugar in the Port. It is then transferred to large stainless steel or wooden tanks or casks to age for a minimum of two years. After that the Ports are selected for quality and it is determined what types of Port they will become. Obviously, this is a much simplified overview, but it will provide the basics, which can lead one to further exploration and reading.