a large number of grape varieties are grown in the douro region, most of them local portuguese grapes. for a long time, the grape varieties grown in the douro were not very well studied. vineyards of mixed plantation were the norm, and most of the time, the vineyard owners didn't know which grape varieties they were growing. a pioneering effort were made in the 1970s which identified touriga nacional, tinta roriz, touriga franca, tinta cão and tinta barroca as the prime dark-skinned grape varieties. tinta amarela and the teinturier sousão has later come to be included among the varieties that attract the most interest. this work was important for creating the new wave of top douro wines and has also led to a greater focus on the grape varieties that go into port wine. most top quintas now replant with single-variety vineyards and focus on a limited number of varieties, but older, mixed vineyards will remain in production for many decades to come.