Dao is one of Portugal's most promising wine regions, but has had a reputation for rarely delivering on its full potential. This is slowly changing, as international wine media attention and improvements in production (and marketing) have helped the region to start shining. The top Dao wines are now some of the most highly rated in Europe, winning consistent praise on both sides of the Atlantic.
The Dao viticultural region lies south of the better-known Douro, source of Portugal's most famous wine, port. It takes its name from the Dao river, along which the majority of the region's vineyards are located. The Dao is a tributary of the larger Mondego (Portugal's longest river) and the Pavia, Alva, Criz, Coja, Carapito, Satao and Ceira rivers also flow through the region. However, only one is significant enough to have the local DOC named after it. The reason is granite – the tough, crystaline rock through which the Dao river has carved its path over many millennia.
To the north, south and east of the Dao Valley are the granite mountains of eastern Beiras. These are the same peaks which separate Beira Litoral (coastal Beira) from Beira Interior (inland Beira), and the Dao and Douro rivers. As a result of this protected position, the climate along the Dao is relatively mild, stable and consistent between vineyard sites. Naturally, this creates a homogenization of the region's terroir; whether this is a bad or good thing is open to debate.
The majority of Dao's quality vineyards are situated at altitudes between 500 and 1500ft (150–450m) above sea level. This elevation raises the vines out of the valley's shadows and towards all-important sunshine, allowing them to maximize their photosynthesis time during the day. It also increases diurnal temperature variation, helping the grapes cool down at night, which they must do to retain the acids so desirable in wine.
The biggest name in Dao wine production is Sogrape, the first wine company off the mark after Dao's restrictive wine laws were lifted at the time of the 1989 vintage. Sogrape also happens to be the largest Portuguese wine producer, having firmly established itself in the second half of the 20th century through the remarkable success of its Mateus rose wine. The company invested heavily in the Dao area, most obviously at the Quinta dos Carvalhais (The Oaks Estate), which now processes several million liters of wine each vintage. The quinta ('farm' or 'estate') has only a modest acreage under vine and much of its wine is made from grapes bought in from the surrounding area, much like the old system created under the Salazar regime.
Arguably, the finest red wines from Dao today are deep reds made from Tinta Roriz and Touriga Nacional, two of the key grapes used to make port wines. Jaen and Alfrocheiro Preto are two other common red wine grapes here, along with large quantities of lesser grapes such as the memorably entitled Bastardo and the Baga that dominates plantings in Bairrada to the west. White wines are also produced in Dao, with the finest examples based on Encruzado, the region's most widely planted light-skinned grape variety.