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August 2018 WINES&VINES 39 PRACTICAL WINERY & VINEYARD WINEMAKING 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -0.5 -1.0 -1.5 2.0 1.5 1.0 0.5 0 -0.5 -1.0 ANOMALY (°F ) ANOMALY (°C) tion. The climatic conditions characterized by low solar radiation coupled with the potential for reduced photosynthetic surface due to downy mildew attacks are common in this type of vintage, resulting in low sugar produc- tion and inadequate degradation of organic acids. The simultaneous action of fungi such as Botrytis cinerea, resulting in mold formation or, worse, the action of fermentative yeasts and acetic bacteria responsible for development of sour rot provides an additional phytosanitary aggravation of a situation that is already dif- ficult to manage. Botrytis cinerea is a fungus widely found in temperate viticultural regions where moisture is not limiting during the fruiting season. The presence of water on the surface of the grapes, together with temperatures between 15° and 25° C, triggers the mycelium growth. Under conditions of alternating dry and humid peri- ods, the disease proliferates in its "noble" form. The alternation of warm and windy afternoons with cold and humid mornings, particularly with the presence of loose clusters of grapes that are well-ventilated, allow development of so-called "noble rot." This particular form of B. cinerea infections developing on certain cultivars under a spe- cific set of environmental conditions can re- sult in wines of high quality and commercial value, such as Sauternes-Barsac and Hungar- ian Tokay. However, this form of mold is an exception that can be achieved only by com- bining a favorable climate with specific grape varieties. More often, the winemaker is left in the position of vinifying grapes that have ripened under poorly ventilated conditions, resulting in Botrytis infections that produce gray mold. Grapes affected by this dangerous pa- thology result in must with the following characteristics: • Low sugar content: Sugar concentra- tion is weak due to the degradation caused by fungus. • Clarification difficulty due to in- creased viscosity and suspended solids. • Organoleptic and aromatic deviations due to the presence of mold metabolites. • Greater degradation of L-malic and tartaric acids, resulting in a decrease in total acidity. • Risk of color alteration due to the action of fungal laccase enzyme. • Higher-than-normal concentrations of acetic and citric acids. • An increase, occasionally consistent, in the concentration of gluconic acid, as much as 3-4 g/L. • A low concentration of nitrogen and presence of toxins that alter yeast metabolism. The processed must of grapes affected by gray mold might fall within different "criticali- ties." Among these, there almost certainly will be difficulties with the fermentation, in large part due to depletion of nutrients, with sources of YAN such as ammonium and amino acid nitrogen having been depleted by the fungal pathogen for its own metabolism. Moreover, the increase in gluconic acid will make it difficult to protect the must from oxi- dation because the increased total SO 2 will be high. Thus, at the same level of total SO 2 , a must with high gluconic acid will result in a bound SO 2 level that is greater than the same must produced from healthy grapes. KEY POINTS The recent increase in average temperature, commonly called climate change, has brought vintages characterized by opposite and extreme conditions. Extreme weather conditions such as high rainfall, low or high temperatures, or water shortages make it increasingly important for the winemakers to have an in-house quality control all over the winemaking process obtaining, in this way, analyses in real time. Besides the regular analyses, to manage alcohol fermentation, yeast-assimilable nitrogen (YAN) and gluconic acid have acquired increasing importance to achieve an optimal wine quality in adverse conditions. YAN allows the winemaker to take important decisions in order to avoid stuck fermentations or "off" flavors. TEMPERATURE ANOMALIES IN EUROPE, 1960-2015 Figure 2: Temperature anomalies in Europe calculated between July and October. 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015