Port anD the Douro 61Aspect and exposure: The angle at which the sun’s rays strike the soil and the duration
of insolation are particularly important during the maturation period. In the cooler
westerly sub-sections of the Douro, a southerly exposure is favoured over a north-facing
slope whereas in a hot year south-facing vineyards in the Douro Superior may suffer
from excess heat. For this reason points vary from minus 30 for a north-facing property
in sub-section 1 (above) to plus 100 for a slope facing south in sub-section 4.
Stoniness (soil texture): Stonier soils allow rainwater to penetrate, and the schist both
reflects sunlight and acts as a heat reserve, thereby modifying the microclimate below
the vine canopy. Stony soils are therefore awarded 80 points with no score being given
to soils lacking in stone.
Age of the vines: Older vineyards generally yield less but produce more concentrated
wines. For this reason vines less than five years old are excluded altogether from Port
production (with implications for the methods of grafting outlined below). Those
between four and twenty-five years of age receive 30 points and those more than
twenty-five years old are given 60 points.
Shelter: The narrow tributaries of the Douro are more sheltered and therefore hotter than
the exposed planaltos north and south of the river. Consequently, the most sheltered sites
are awarded a score of 60 points as opposed to the most exposed, which receive zero.
Vine density: Higher densities generally reduce the vigour of each vine, the theory being
that as every plant yields less it produces grapes of better quality. In the past, densities
above 5,700 vines per hectare were penalised whereas densities between 4,000 per
hectare and 5,700 per hectare were awarded 50 points. Now all vineyards with a
density above the legal minimum of 3,000 vines per hectare are awarded 50 points.
After taking each of the variables into account, the maximum number of points that can
be awarded to any one vineyard is 2,031, with the minimum being a theoretical (but
impossible) minus score of 3,129. After a great deal of number crunching, each holding is
classified according to the total number of points, as follows:
Class A: above 1,200 points
Class B: 1,001–1,200 points
Class C: 801–1,000 points
Class D: 601–800 points
Class E: 401–600 points
Class F: 201–400 points
Class G: 1–200 points
Class H: 0 – minus 200 points
Class I: minus 201 points – minus 400 points