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38 WINES&VINES August 2018 WINEMAKING PRACTICAL WINERY & VINEYARD A n increase in average temperatures in recent years is profoundly chang- ing climatic parameters that influ- ence agricultural activities, including rainfall patterns, maximum and minimum temperatures and humidity. The phenomenon, commonly referred to as climate change results in extraordinary weather parameters and an increase in the frequency of vintages marked by high tempera- tures and water scarcity as well as vintages characterized by low temperatures and high levels of rainfall. With these kinds of extreme vintages, the analyses of yeast-assimilable ni- trogen (YAN) and gluconic acid acquire in- creasing importance in the winemaking process in order to maximize quality in a finished wine. Temperature anomalies have been mea- sured for decades during the ripening period of grapes in North America and Europe (Figure 1: "Temperature Anomalies in North America, 1960-2015" and Figure 2: "Temperature Anomalies in Europe 1960-2015"). The past 15 years have been characterized by an in- crease in abnormalities compared to the aver- age temperatures measured since 1910. Extreme meteorological phenomena are reflected by diametrically opposite weather trends in 2003 and 2014. In 2003, Northern Europe experienced one of the hottest vintages ever, with average temperatures from May to October far above the standard, accompanied by extreme drought. In 2014, France had one of its rainiest years ever, with precipitation up 140% from June through August. In July 2014, Milan, Italy received about 300 mm of rain during a 15-day stretch, compared to a 73-mm average for that period. Climate impact on must What are the effects of high temperatures and water shortages on the grape-ripening phase? Conversely, what are the effects of low tem- peratures and high precipitation? While the characteristics of these situations differ, both have a strong impact on the must and are equally difficult to manage in order to achieve optimum fermentation. Since the enologist is unable to influence meteorological factors, optimal management of the alcoholic fermen- tation is crucial to preserve the aromas, avoid- ing organoleptic deviations that are difficult to "recover" in subsequent steps. Besides the analyses of total acidity, sugar, pH and volatile acidity, which must be per- formed on an increasingly time-oriented basis, the analyses of YAN and gluconic acid become fundamental. These two analyses are valuable tools in the hands of enologists, who can use them to manage the delicate process of alco- holic fermentation. High rainfall and low temperature Grapes harvested in vineyards characterized by high rainfall and low temperatures have a deficit of phenolic and technological matura- Winemaking in the Era of Climate Change Determine yeast-assimilable nitrogen and gluconic acid for optimum alcoholic fermentation management By Simone Bellassai TEMPERATURE ANOMALIES IN NORTH AMERICA, 1960-2015 Figure 1: Temperature anomalies in North America calculated between July and October. 2.5 2.0 1.5 1.0 0.5 0 -0.5 -1.0 -1.5 1.5 1.0 0.5 0 -0.5 -1.0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 ANOMALY (°F ) ANOMALY (°C)