| February 15, 2012
Image Source: http://www.avalonwine.com/images_articles/grapes_med.jpg
Study after study has indicated that the earth is undergoing a state of climate change. Regardless of how you believe it was caused, be it by anthropogenic sources or a natural cycle of the earth, I think we can all agree that the earths’ climate is changing, though it’s likely the change will vary depending upon where on the earth’s surface one looks.
In regards to viticulture and wine, studies have found that temperature affects the rate of development of the grape, which includes sugar accumulation, acid loss, and the synthesis of color and flavor components. The levels of components such as anthocyanins, phenolics, tannins, and other antioxidants affect color, bitterness, and flavor, and the ratios of which can alter the overall quality of the finished wine.
One major concern about global warming and climate change is that it could shift the timing of the growing season, which would ultimately decrease the quality of the finished wine from earlier grape harvests at high temperatures. Certain parts of the globe could also be undergoing a transitional cooling, which would result in even more variability and uncertainty in the growing season of grape varieties. There has been very little research regarding the effect of climate change on the development of grapes, however some greenhouse studies have shown that when grapevines are exposed to higher temperatures, they produce significantly lower levels of anthocyanins, while sometimes even degrading the anthocyanins that remain. This results in an overall decreased quality of wine, which would have profound implications on the price and overall economic health of the winery.
It is with cool-climate varieties of grapes, such as Pinot Noir, that scientists speculate will be most affected by rising temperatures caused by climate change. One recent study aimed to collect detailed temperature and light measurements in a Pinot Noir vineyard, in order to analyze their effects on grape skin composition, while providing suggestions on possible changes to vineyard management practices. They included light exposure in addition to temperature, since scientists have speculated that light intensity may have an equal, if not greater effect on the development of the grape, due to either increased temperature, color bleaching, or both.
The overall results of this study were that heat accumulation during the postharvest season prior to the year of maturity, and heat from bloom to veraison were both negatively correlated with concentrations of anthocyanins, tannins, and iron-reactive phenolics. This means that high temperatures in the previous postharvest season and high temperatures during the period of bloom to veraison led to decreases in anthocyanins, tannins, and iron-reactive phenolics, which result in an overall lower quality finished wine.
Another important finding of this study was that light exposure explained more of the variability in total phenolics and tannins than the temperature. The study found that high levels of light resulted in lower concentrations of anthocyanins, tannins, and total phenolics. This means that trellising plays an important role in this result, in that grapes that are more exposed to the sun have lower concentrations of anthocyanins, tannins, and total phenolics than grapes trained on a different trellis system that allows more shading.
Due to these results, it may be recommended that vineyard managers adopt an approach that increased the shading to the grape clusters on the vines, by increasing the leaves in the canopy to protect the clusters against intense light and temperature exposure. This may mean changing the trellis system in the vineyard, and perhaps also irrigation practices, in order to create shadier and cooler conditions for the Pinot Noir grape (in the Sonoma/Napa region of California; though the theory can be applied to any location) to grow and develop with ideal phenolic levels as climatic conditions continue to warm as the models suggest.
For more details on this study, please visit The Academic Wino for more.
Becca Yeamans is the owner/writer of the science-based wine blog, The Academic Wino, as well as the Tasting Room Manager at a vineyard in central Virginia. With a Bachelor of Science in Biology and a Master of Science in Environmental Science, her solid background in science and research allows her to approach wine blogging with a unique style that is both informative to those in the industry, and entertaining for those simply wishing to learn.