A classification system has been applied to all Douro vineyards for the production of port wine since 1940. A comprehensive and very detailed point system evaluates twelve different components and leads to an overall classification in 6 quality groups (A-F).

Altitude:
Since different climate factors influence the development of vineyards located at different alti­tudes, the awarded points vary between + 240 (up to 150 m) and - 900 points (for areas above 650 m).

Zone:
The three Douro sub-regions are divided into five zones with their respective zones in accord­ance with climatic conditions:

Zone 1: the higher elevations of the Baixo Corgo, north of Régua with the coolest, most Atlantic climate:
0 to + 260 points

Zone 2: the north bank of the Douro River from Barqueiros to the Corgo River (including Régua), and on the south bank und from Barro to the Vilar River: - 50 to + 250 points

Zone 3: on the north bank from the mouth of the Corgo to the Ceira River (near Govinhas) and
on the south bank from Vilar to the Tedo River: - 50 to + 460 points

Zone 4: the heart of the Cima Corgo and parts of the Douro Superior, from the rivers Ceira and Tedo to the Saiấo Valley (Pocinho). This also includes the tributary valleys of the Tavora, Torto, Caedo, Pinhấo and Tua rivers: - 50 to + 600 points

Zone 5: from Saiấo to Barca d'Alva ( the majority of Douro Superior): + 140 to + 450 points

Yield:
Based on the principle that higher yields bring lower quality, cultivation areas yielding 600 l per thousand vines get a maximum of 120 points while at least 900 points are deducted where yields exceed 1,800 l per thousand vines.

Soil type:
Up to + 100 points for slate soil, - 100 points for "transition forms ", - 250 points for granite, and - 400 for alluvial soil (which practically no longer exists since the damming of the Douro).

Type of training:
Because the vines that are grown close to the ground yield better maturity, vineyards with a maximum vine height of 0.8 m receive 100 points. Pergola sites (as they are typical for Vinho Verde) are excluded from the Douro classification.

Grape varieties:
In the original evaluation system of 1940 the numerous grape varieties of the Douro were classi­fied in five groups from "very good" (+ 150 points) to "poor" (- 300 points). This classification has become much simpler. The valuation nowadays only includes "recommended " or simply "permitted" types of vines.

Slope gradient:
Flat vineyards receive no points and a slope incline of more than 35 degrees is rewarded with up to + 101 points.

Exposure:
In the cooler western areas, more points are given for southern exposure, while areas with strong exposure to the sun can be a disadvantage in the hot zones of the Douro Superior. The points awarded for exposure within a zone range from - 40 to + 100 points.

Stony ground:
Because stony grounds allow for the absorption of moisture and slate reflects sunlight and stores heat to create a special micro-climate, up to + 80 points are awarded for stony soil.

Age of vines:
Vines that are younger than four years are excluded from port wine production. Vineyards with vines aged 25 get + 30, and + 60 points are awarded for ages over 26 years.

Shelter:
The narrow valley locations and river estuaries are protected from wind and can therefore be hotter than vineyards in higher altitudes. They are awarded + 60 points for this.

Planting density:
It is generally assumed that a high planting density leads to lower stress on every vine and con­sequently to better quality. However, a density exceeding 5,800 vines per hectare is considered unfavorable in the Douro region, while planting densities between 4,000 and 5,700 vines per hectare are rewarded with + 50 points. (Nevertheless, the yield is calculated per 1,000 vines, and not per hectare).

A total is calculated from all these components and can range from a maximum of + 1,661 points to a theoretical minimum of - 2,440 points.

The following scoring limits apply to the classification into the six quality groups: