Growing Vines in the Douro Valley

• Posted on 2 October 2024
• 0

In total, Portugal is about 90 miles wide and about 300 miles north to south. Most of the population lives on the coast, either in Lisbon, the capital, or in Porto. Traveling due east of Porto for about 60 miles is where you find the Douro Valley, which then expands into Spain for another 30 miles, and three different wine regions. Going from west to east is Baxio Corgo (lower Corgo), Cima Corgo (upper Corgo), and Douro Superior. The “lower” and “upper” indicate the side of the Corgo River’s confluence into the Douro River, where these wine regions sit. Lower indicating downstream, and in this case, closer to the Atlantic.

You would think that since this wine region’s valley is only 60 miles away form the huge Atlantic Ocean that the ocean would have a significant influence over the valley’s climate. It does, to an extent. Like the Loire Valley in France, the western side of the valley is cool and wet, which progresses to more hot and dry, traveling eastward. The Serra do Marão Mountains hold back much of the cold wetness, resulting in a more generically continental climate over the Douro Valley, with progressively more extremes from west to east. Thus, it makes sense then that the hottest section, the Douro Superior on the east, would start harvesting well before the cooler, wetter Baixo Corgo on the west.

What are the hazard risks in the Douro Valley? It seems a bit of climate change is causing this region to heat up as a whole, and become drier. Generically, the region has schist on top of shallow topsoil with low organic matter. This kind of soil does not hold water; it passes right though. The determining factor between which section of the valley is appellated for high quality wines and which is not is the vertical layers vs horizontal schist layers. The vertical layers allow the vine roots to push through the layers in search of water. Having a region increase in temperature means the vineyard managers will have to choose rootstock that is accepting of drought-like conditions, so fast/deep growing can get established. The Portuguese viticulture government, IVDP (Instituto dos Vinhos do Douro e do Porto), in 2019, has relaxed the irrigation regulations. If the vines are in a state of hydric stress that jeopardizes quality (different than quantity), then the vineyard is authorized to irrigate, as long as the producer notifies the IVDP. But as long as humidity is going down, then the fungal pressures will also go down, meaning less need to apply sprays.

The other part of the increase in temperature hazard comes later in the growing season upon the fruit itself. Grape varietals all have a different velocity for ripening over the growing season. Let me take this apart a bit more for you here. Harvest happens at the point when the berry can produce the most balanced wine. Key considerations for determining balance are acid, color, phenolics (flavors), sugar (the potential for alcohol), and tannin for the style of wine intended. (This IS A HUGE RABBIT HOLE which I may come back to in another blog). Generically then, the warmer seasons will cause the berry to gain sugar and lose acidty faster than the time it takes for the berry to develop enough color and flavors. This is why having a big change from day to nighttime temperatures is so important. The berry has time to stop producing sugar while continuing to progress gaining flavors. There are a few measures a vineyard can take. First is to plant vines at a higher elevation (cooler temperatures). The second might be to plant on north facing slopes that are cooler and get less sun.

On the western side of the Douro Valley is the Baxio Corgo sub region, which starts in the foothills of the Serra do Marão Mountains and goes east to the confluence of the Corgo and the Douro rivers. The region is identified as being the coolest and wettest, as it has the higher amount of Atlantic Ocean influence. It receives 900mm of precipitation per year, well above vines’ needs per annum, even with the mountain barrier.

On some years there is a hazard of too much water. Early in the season this could mean frost damage. Planting on the middle part of the slopes helps to alleviate being too cold, as cold air slides down into the valley and the slope is warmer above the fog. Later in the season, too much rain could mean blotted, damaged, diseased fruit. Harvesting ahead of a thunderstorm could help, but there is a risk the fruit may be unripe.

This geographically accessible region consistently produces about 50 percent of the volume of wine across the Douro Valley, (Cima Corgo out produces the Douro Superior).  Good to mid-level, high-volume ports, white wines (because it is cooler here—helps keep the acidity better), white ports, pink ports, and a few red wines are made in this region. 

Until the end of the 18th century, the narrow gorge was obstructed by a waterfall formed by gigantic outcrops of rock, making it impossible to navigate upstream into the remote eastern reaches of the Douro. In 1780, the arduous work of demolishing the stone slabs began. By 1789, the first vessels were able to pass through the gorge, and in 1791, the work of clearing the channel was finally completed, although the task of negotiating the fast-running rapids of the Cachão remained extremely hazardous. Since the river was the only viable means of carrying wine out of the valley, there had been few vineyards in the area east of the Cachão.

Slightly warmer and drier than the Baixo Corgo, the Cima Corgo receives 700 mm rain per annum. It is considered the heart of the Douro, as many of the premium and super-premium ports were developed here. Douro’s tributaries include Rio Tedo, Rio Tavora, Rio Torto and Rio Tua. All of which have carved out winding waterways, each with distinct microclimates. The best vineyards are the steepest of slopes right on the river. 

In both Baixo and Cima, and to a lesser extent Douro Superior, 30 degree or steeper slopes are not uncommon for planting vineyards. Narrow terraces supported by walls of dry rock, called Socalcos, became the traditional way of planting a vineyard. Over time, the walls need labor for repairs, which adds to the cost of wine. UNESCO has protected these walls in the Douro, meaning the vineyards can not be converted to any other layout.

The hottest and driest of the regions is Douro Superior, also known as Upper Douro. It is by far the largest land region, extending from Cima Corgo to the Spanish boarder. Plantings, however, are sparce. It receives only about 450mm rain per annum. The region plants in much lower densities, reducing water competition between plants.  Drought is a frequent concern. 

The advantage here is the land. In places it is much fatter, allowing for cost-saving mechanization. Plantings here are increasing. Vintners are producing good to premium red blends in this region.