Compared with most vineyards in Europe, a vineyard at 1,500m altitude is colder, while air composition can be different and sunlight intensity is higher, especially in semi-arid climates. But so far, European viticulturists have tended to discard the influence of altitude on aromas and flavours, believing than any effects are simply due to the cold. A conversation with Dr Laura Catena of Bodega Catena Zapata in Mendoza, Argentina, reveals a different story.
From a European point of view, South America is far away. This might be the reason why so many Europeans — and others — are unaware of the scientific research done by Catena Institute of Wine. The Institute, founded in 1995 and financed 50 percent each by the Argentine Government and Bodega Catena, has done impressive research on the influence of altitude, solar ultraviolet-B light (UV-B) and other factors on grape berry components.
“High altitude vineyards’ environmental conditions affect the oenological quality of berries in a significant way,” says Dr Catena. “We found a lot of influences besides cooler temperatures.” She points to a long list of publications by the Institute, where 10 scientists work. Dr Catena, the managing director of Catena Zapata, is both a medical doctor and a biologist.
The most important aspect affecting the grapes, besides the lower temperature, seems to be the increasing UV-B, the most energetic fraction from sunlight. Since UV-B light is very strong at high altitude, it can damage living tissue. The plant defends itself by producing compounds that protect it, but which are also beneficial for grape quality, such as amino acids, proteins and lipids. But the influence is not linear. While the increase in UV-B from 500m to 1,000m is quite modest, the further increase at 1,500m is dramatic. Most Argentine vineyards grow at between 600 and 1,500m.
Federico Berli from the Catena Institute and his team have been running experiments since 2006 on the effect of UV-B on grapevines. The experiments showed that UV-B resulted in fewer leaves per shoot, shorter shoots, less leaf area, less chlorophyll and less photosynthesis. On the other hand there were thicker leaves, more phenolic compounds and an increase in abscisic acid (ABA, the stress hormone), terpenes and antioxidant capacity. The leaves also showed higher levels of pigments that protect against light damage.
Of course, all these changes resulted in different grapes. The fruit had higher levels of anthocyanins, as well as a higher phenolic content in the berries. Overall berry growth and yield, however, were reduced. Mendoza’s wine-growing regions planted above 1,000m tend to develop higher-quality berries because of the greater accumulation of polyphenols and aromatic compounds in the berry. These higher polyphenols and aromatic components translates into a wine with a darker colour, more complex flavours and longer ageing potential. “Of course we are happy about the fact that our wines from high altitude, like the Adrianna vineyard at 1,450m, have better phenolic structure,” says Dr Catena.
Viticulturists need to work differently in high UV-B environments, as the UV-B causes stress. Using water deficits to control berry size and ripeness may have some effect, but less than it might in a lower UV-B environment. There is a general risk: evapotranspiration — whereby water not only evaporates from the soils but also from plants — demand can be so high that even if there is water in the soil, the vines are not able to keep up with the evapotranspiration rate. This can lead to unripe tannins, which the French call “blockage”.
High altitude brings another risk: fresh and intense aromas combined with the risk of unripe tannins can lead winemakers to harvest late, because there is less risk of losing fresh aromas. This can produce wines with very high alcohol contents. While sensitivity to this has risen in Argentina during the past five years, there are still plenty of 15 per cent ABV and more wine on the market, surprisingly often coming from high-altitude vineyards.
More to learn
The Catena Institute’s spectrum of scientific work is wider than research on UV-B influence alone. Its researchers have published important papers on the Malbec grape variety, looking at anthocyanin profiles in selected Malbec, and on the phenolic composition of Malbec. Other research had important results. In cooperation with University of California, Davis, wines from five Argentine clones were compared with reds from five French clones. The study’s message, presented in 2015, was that Argentina has more desirable Malbec selections than France does. Since then, quality-oriented Argentine winemakers ceased importing French Malbec clones and have chosen to use their own.