Winetech Technical Yearbook 2022

study. The harvest time was significantly influenced by altitude and cultivars, ranging from 6.27 to 7.16 days for every 100 m of elevation, while budbreak time ranged from 0.85 to 2.88 days for every 100 m. In other studies, a decrease of 4°C in mean tempera tures of vineyards at higher altitudes, delayed harvest by up to two months in Cabernet Sauvignon. Higher thermal amplitude means there could be more tempera ture extremes such as an abnormally hot day in winter or freezing temperatures that can cause cold injury in late winter or early spring. One downside of extended phenological stages is for example at budbreak, the vulnerable plant structures are exposed to the risk of hail damage or frost for an extended period of time during the cooler part of the growing season. On the upside, cultivars with shorter growing cycles may produce better quality grapes as the slower ripening period leads to better accumulation of aromatic and phenolic compounds by the time sugar ripeness is reached. Altitude and physiology Extreme climatic conditions affect grapevine physiological pro cesses. Extremely warm temperatures can impede vegetative growth and reproductive development which impacts yield and fruit quality. It is also known that photosynthesis is drastically reduced at temperatures above 35°C. On the other hand, extreme cold can affect fruit set and carbon accumulation in berries, as well as reduce photosynthesis. Higher altitudes are more likely to experience extremely cold days, which poses a frost damage risk, especially during sensitive stages, such as bud break or flowering. Other studies show that increased UVB levels lead to a decrease in leaf area and reduced berry size and fruit yield. It also causes an increase in grape berry skin thickness as more anthocyanins (which act as photoprotective pigments) accumulate in the skin. Altitude and grape berry composition An advantage of cooler temperatures at higher altitudes is extend ed ripening periods which can benefit the grape berry composition and quality parameters. Various studies indicate that the main environmental factors that affect grape biochemistry are tempera ture and light exposure. Lower net photosynthesis in leaves subjected to higher UV-B leads to a reduction in sugar accumulation. This does not neces sarily equate to lower Brix at harvest, because increased evapora tive losses can increase sugar concentration, while reduced berry size can have the same effect.

Research shows there is a positive correlation between elevation and the production of anthocyanins, flavanols and stilbenes which favour colour intensity, anthocyanins and aromas in the resulting wines. At cooler temperatures, there is less malic acid breakdown in berries, and the acidity in the final wine tends to be more com pared to wines from grapes grown at warmer temperatures. In a sensory evaluation of Merlot and Cabernet Sauvignon wines, made from vineyards at varying altitudes, the wines from the higher altitude sites scored highest as the quality in terms of taste and aroma intensity were better. CONCLUSION Terroir and the location of a vineyard site play an important role in wine style. Establishing vineyards in higher altitude sites is not possible everywhere, but it could be a means of adapting to a changing climate and to mitigate the effect of climate change on grapevine production. Higher altitude sites have lower average temperatures with a higher thermal amplitude and increased ra diation. These factors result in a delayed growth cycle, reduction in vegetative growth and berry size, along with increased acidity and a higher concentration of anthocyanins, colour and aromas in resulting wines. One should keep in mind that the climatic conditions at higher altitudes can present certain challenges that could negatively affect the grapevine. Cultivar selection is critical, and canopy man agement and viticultural practices should be carefully considered and fine-tuned to the site and ultimately the required wine style, in order to produce quality fruit. REFERENCE Arias, L.A., Berli, F., Fontana, A., Bottini, R. & Piccoli, P., 2002. Climate change effects on grapevine physiology and biochemistry: Benefits and challenges of high altitude as an adaptation strategy. Frontiers in Plant Science 13, 835425. https://www.wineland.co.za/high-altitude-vineyards/

For more information, contact Lucinda Heyns at lucinda@winetech.co.za.

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WINETECH TECHNICAL YEARBOOK 2022