Most of the Demarcated Region, particularly along the Douro River and its tributaries, has schist soils with some granite outcrops in the region’s border areas. The schist soil, rich in nutrients, helps preserve heat and erosion and has the useful property of retaining water.
The schist soil of the Douro vineyards has the essential quality of viticultural soils – the ability to allow the vines to develop while moderating their access to water and, consequently, the vine’s yield, producing more robust and concentrated wines.
With deep valleys protected by mountains, the region’s climate is characterised by freezing winters and hot, dry summers. The dry climate, combined with the small, thick-skinned berries that characterise the Douro’s traditional varieties, favours the production of wines of extreme richness and depth.
The Douro Superior, being the driest of all sub-regions, is the source of many of the finest Douro DOC port wines and table wines.
The Grape Varieties
In the Douro, the diversity of native grape varieties is immense, with around 100 different varietals identified. This diversity of plants allows the adjustment of the best grape varieties to the region’s diverse microclimates and soils. A reglementary law lists the authorised and the recommended grape varieties.
As far as productivity is concerned, the region is not characterised by having very productive varieties. The maximum allowed yield is 2225 litres per acre (around 3,000kg/acre), and the average productivity is approximately 1,215 litres per acre (1,650kg/acre).
In the 20th Century, a study and analysis of the grape varieties planted began and concluded that the best red grape varieties for producing Douro and Port wine are: Touriga Nacional, Touriga Franca, Tinta Barroca, Tinta Roriz and Tinto Cão, but also other fundamental varieties and with great expression in the region, such as Tinta Amarela and Sousão.
The production of white wines is essentially supported by the varieties that most contribute to the identity of the Douro blends: Rabigato, Côdega do Larinho, Gouveio, Moscatel Galego, Malvasia Fina and Viosinho.
Vineyard Classification Method
The Estates and vineyards in the Douro are organised according to a classification system based on the physical characteristics of a vineyard and its potential to produce quality wines.
Each vineyard’s total score will dictate its classification, ranging from A to F, whereby with grade A, the vineyard is considered the best.
The factors taken into account in a vineyard’s classification are: