The Douro Valley has been known for centuries as the home of port wine, however, it was not until 1982 that it was granted official Denominacão de Origem Controlada (DOC) classification. Located in the north-east of Portugal, between Barqueiros and Mazouco, on the Spanish border, Douro takes its name from the river that flows through the valley. It is protected from the harsh Atlantic winds by the Marão and Montemuro mountains to the north and west, and as a result, it is extremely hot during the summer months, with temperatures often reaching the 100-degree (Fahrenheit) mark and higher. In the winter, however, temperatures can drop to freezing. The soils in this region consists primarily of granite and slate which allows moisture to seep in, and also gives the vine roots a place to grow. According to sources, Portugal's Instituto da Vinha e do Vinho (Institute of Vine and Wine) recognizes 341 grape varieties, however within the Douro Valley three native red grape varieties are prevalent: Touriga Nacional; Tinta Roriz; and Touriga Francesa. While not as common, some white and rosé wines are also produced in the region from grape varieties such as, the Rabigato, Viosinho, Gouveio and Codega.