the area is home to several dozen varieties of indigenous grapes, with the majority of wine production being made from the touriga nacional, tinta roriz, jaen, alfrocheiro preto and encruzado. 80% of the region's production is in red wines, with doc regulations stipulating that at least 20% of the production must be from touriga nacional. some of the top reserve wine may carry the designation "dão nobre" (meaning noble dão). another reserve designation, "garrafeira," requires wines to be 0.5% higher in alcohol content then the 12.5% minimum and to spend at least 2 years in aging in oak. the maximum yield for red wine grapes is 70 hl/ha.