Indigenous to Portugal, Touriga Nacional is the finest and most revered grape for producing vintage port. Despite the low yields from its small grapes, it plays a big part in the blends used for ports, and is increasingly being used for table wine in the Douro and Dão.
The tiny berries of Touriga Nacional have a high skin to pulp ratio which heightens the amount of extract in the wine. The grapes known to produce intense, very aromatic wines with high tannin content. In the Douro it is grown in searing heat in steep schist vineyards that are more rock than soil. The alternative name of 'Mortagua' pays tribute to these harsh conditions. The wine is usually trained under one of the Guyot systems, and needs severe pruning to keep it under control.

 

In contrast, the vine produces just a few bunches of blue-black grapes which vary in size from small to tiny on the bunch. The vine is vigorous; though producing a lot of foliage and fewer bunches of grapes than other varietals. In the late 1990s there were 2,760 hectares of Touriga Nacional in Portugal.
Thus yields are among the lowest of any commercial grape variety. It constitutes a small percentage in the blend of most Port wines and due to its low productivity accounts for only 2% of the Douro Valley's vines.
In recent years, scientists have been working on cloning the Touriga Nacional to produce vines that are able to pollinate better with the goal of increasing yields by 15% and sugar content by 10%. Grown for quality rather than quantity, Touriga Nacional produces wine with finesse, structure, body and warmth, and yields dark, concentrated, massively tannic and aromatic wines, with an intense black fruit fragrance.
The depth and richness of flavour in the best Port wines owes much to the flavours of Touriga Nacional, but Ports nearly always contain a mixture of varieties. In fact about 80 varieties are authorised for inclusion.
The most common grape varieties in red Port are: Touriga Nacional, Touriga Francesa, Tinta Barroca, Tinta Roriz, Tinta Cão, Souzao, Tinta Amarela and Mourisco Tinto.