Wine Astringency with a Flavor of Climate Change

Significant Changes

Plant mortality is not the main concern in this industry, as many grape varieties are well-adapted to withstand drought conditions and even demonstrate an impressive ability to acclimate to variable environmental conditions. Instead, the issue is that these environmental conditions have a profound impact on the grape’s chemical composition, and subsequently, on the character and quality of the wine produced from them. This intense connection is captured by the term, terroir, which represents the specific environmental conditions in a given region - such as temperature, humidity, rainfall, soil type and more - that impart a unique signature to the resulting wine. Over the past decade this signature has been consistently compromised due to escalating climate change, resulting in less rainfall, increased temperatures and heightened occurrence of extreme events such as fires and droughts.

Temperature during the growing season has a crucial effect on grape composition, hence influencing the quality of the resulting wine. Many studies have found that an increase in temperatures leads to an increase in the concentration of sugars in the grapes and a decrease in the concentrations of acids as well as other substances, such as tannins, anthocyanins, and flavonoids. Subsequently, during wine production, the sugars turn into alcohol as a result of yeast fermentation, while acids and other substances enrich the wine with additional layers of flavor, color, aroma and mouthfeel.

As a result, wines produced from overly sweet grapes, poor in these accompanying compounds and substances will have a high alcohol content and will lack the additional characteristics that define the uniqueness of quality wine. Consequently, traditional quality wine producers are apprehensive about their wines losing their unique character, or their distinctive terroir.

Besides the increase in average temperature, climate change accelerates grape growth and compresses the ripening stages - in other words, the winter concludes earlier, thereby shortening the time intervals between the different stages of fruit development. Specifically, in some regions in the northern hemisphere the ripening season is advancing from September to August. This phenomenon also contributes to the growing of grapes with a high sugar concentration. While vintners could harvest the grapes earlier to prevent sugar development, this would also preclude the accumulation of the additional substances mentioned earlier, which typically develop at the end of the season.

Drought Days

Another phenomenon related to climate change is an increase in the frequency and severity of drought years. Drought can have a fatal impact on the vines, particularly in regions where artificial irrigation practices of agricultural crops are uncommon, such as many of the wine-producing regions in Europe and North America. With some grape varieties demonstrating resilience to drought, vintners could preserve the industry by adjusting their agricultural practices and strategies, for instance, by planting and cultivating more drought resistant varieties or by introducing irrigation systems. However, extreme water scarcities may have long-term consequences on the vines and a profound impact on the functioning of the vineyards.

Furthermore, in contrast to the rise in temperatures, the impact of drought periods on grape quality is not straightforward. It appears to be influenced by multiple variables, including grape variety, drought duration and severity, the timing of the drought in relation to the growing season and other concurrent environmental conditions.

During early grape development, prior to color change, grapes are connected to the vine’s xylem - the primary vascular system for water transport from the roots to all parts of the plant - and are directly affected by its condition. Thus, a water shortage at this stage may result in small, shriveled grapes. Interestingly, and in slight contrast to the typical approach with most crops, vine growers often intentionally reduce grape irrigation during this growth phase of growth in order to produce smaller grapes. This strategy increases the relative proportion of grape skin, enriching the wine’s quality since the skin contains most of the accompanying substances that contribute to the flavor and aroma of the wine.

With the onset of the ripening process, when the grapes begin to take on their final color, their main source of sustenance becomes the phloem - a vascular tissue responsible for transporting substances between different parts of the plant. In other words, the water supply to the fruit relies mainly on the regulation by phloem tissue cells, not solely on the vessels of the xylem tissue.

Some studies suggest that grapes under water stress show an increase in the concentration of anthocyanins. Anthocyanins are pigments ranging from red to purple, therefore water scarcity might contribute to the production of red wines with a deep, bluish hue. However, other studies have found no difference in anthocyanins levels under varying irrigation regimes. An Israeli study conducted at Mitzpe Ramon found that the effect varies from one variety to another. Contradicting findings have also been found with respect to the production of tannins (astringents) in the grape skin - these substances are responsible for the tingling feeling, known as astringency, that accompanies drinking wine.

Thus, it seems that the impacts of an extreme water shortage are also related to the duration and severity of the drought, the grape variety, and other environmental conditions during fruit growth. In other words, a lack of water may lead to different, and even contrasting results, under different conditions for different varieties, impacting wine quality in different ways. Further changes in environmental conditions, such as heatwaves, can completely change the equation.

As if that’s not enough, while droughts and heatwaves typically occur in conjunction in the past, recent decades have seen them occur independently, seemingly becoming uncoupled and. A 2016 study found that early grape ripening in western Europe, resulting from rising temperatures, has recently been taking place independently of drought periods. An intensification of this phenomenon may have widespread consequences for the distribution of grape varieties and the use of pesticides, since warm and humid conditions present new challenges in managing agricultural pests.

A Burning Issue

Another phenomenon related to climate change is the spread of fires, particularly in agricultural regions. In California, for example, grapes are exposed to smoke almost every year, due to the increasing frequency and severity of fires. In response, the vines produce substances called phenols, which impart strong, unpleasant aftertastes to the wine during fermentation.

Turning to Israel, how is the wine industry faring? According to agronomist Ariel Nitzan, from Yatir Wineries, and winemaker Oren Kedem, from Assaf Winery, Israel’s climate is already inherently hot and dry, therefore some of the issues mentioned here, such as a low concentration of acids in grapes and recurrent drought periods - an almost integral part of the country’s wine and are effectively managed during grape cultivation and wine production. In addition, in contrast to more traditional wine-producing nations, such as France, where each growing region is allowed to cultivate only very specific, unique grape varieties, Israel adopts a flexible policy towards the composition of grape varieties. Thus, many challenges are overcome through careful selection of grape varieties and rootstocks for vineyard planting. And finally, since Israel’s wine industry is relatively young, it is difficult to track long-term trends of changes over time, such as shifts in ripening times or vine mortality.