Postmodern Winemaking: Rethinking the Modern Science of an Ancient Craft

by Clark Smith

John Gladstones’s brilliant new book, Wine, Terroir, and Climate Change,3 offers an additional perspective on why other climes mature grapes at lower brix. At the risk of oversimplifying a lengthy and insightful discussion, Gladstones points to the notion, rather obvious in retrospect, that grapes are impeded in photosynthesis when highly humid conditions inhibit the evaporation of water. This factor alone might account for the low brixes one sees in ripe fruit in many high-latitude areas, where diurnal summer temperature swings are moderated by longer day length. Absent botrytis, it is rare to see 20° brix in any variety in Germany, and low sugars also abound in humid areas in the upper midwestern and northeastern U.S. Even low-latitude areas such as the southeastern U.S. where weather patterns create high humidity are similarly characterized by low harvest brixes. But in California, where 40°F daily swings are typical, dew points, which correspond to the nightly low temperature, are consequently quite low and daytime air quite dry, and no such inhibition occurs, so fruit sugars up well in advance of ripeness.