Jeremy Weiss* and Jesse Noble
*University of Arizona Cooperative Extension, 1064 East Lowell Street, Tucson, AZ 85721 (jlweiss@arizona.edu)

As temperatures continue to trend higher, winegrape growers and winemakers in warm-climate viticultural regions will increasingly be challenged by the many effects temperature has on fruit composition. Warmer ripening conditions in recent years for such growing regions around the world have resulted in higher sugar concentrations, less acidity from declines in malic acid, higher pH, and changes in aromatic and phenolic compounds, all of which can be particularly affected by daytime maximum or nighttime minimum temperatures. Information that helps identify and minimize these impacts and aids production of well-balanced wines in these regions is needed. Here, we evaluate fruit composition at harvest in the context of time spent during ripening above and below temperature thresholds to test our hypothesis that duration and degree of heat and cold exposure correlate to composition values. For analysis, we use measures of Brix, titratable acidity, and pH for several varieties across multiple vintages from a warm-climate vineyard in southeastern Arizona and accumulated hours of temperatures greater than values between 30 and 40°C (86 to 104°F) and less than values between 10 and 20°C (50 to 68°F), ranges encompassing thresholds reported in previous studies. We calculate temperature accumulations over the 30 days leading up to harvest, basing them on data collected at a meteorological station located approximately one kilometer (0.6 miles) from the vineyard. By determining how exposure to heat and cold during ripening potentially has influenced fruit composition in recent vintages, our work provides an initial model for growers and winemakers in this and other warm-climate viticultural regions with which to predict impacts of temperature conditions in future growing seasons and to consider vine- yard and winery adaptations for production of quality fruit and balanced wines under continued regional warming.

Funding Support: grant NA17OAR4310288 with the Climate Assessment for the Southwest program at the University of Arizona through the National Oceanic and Atmospheric Administration’s Regional Integrated Sciences and Assessments program