Winkler index

The Winkler Index, sometimes known as the Winkler Scale or Winkler Regions, is a technique for classifying the climate of wine growing regions based on heat summation or growing degree-days. In the system, geographical areas are divided into five climate regions based on temperature converted to growing degree-days, and is commonly known as Regions I–V (see below). The system was developed at the University of California, Davis by A. J. Winkler and Maynard Amerine,.

The system is based on both the hypothesis and observations that grapevines do not grow if the temperature is below 50 °F (10 °C). Each day during the growing season (assumed under the system to be April 1 through October 31 in the Northern Hemisphere; October 1 through April 30 in the Southern Hemisphere) are assigned growing degree-days according to the amount that the day's average temperature exceeds this threshold; one degree day per degree Fahrenheit over 50 °F (or with SI units, degrees Celsius over 10 °C is used). All days during the growing season are then added up (all negative values are set to zero), with the sum of the growing degree-days used to determine the region's classification in the original Winkler index as follows:

The system was originally developed for and is used officially in California and was based on the general ripening capabilities and wine styles that can be achieved in the climate due to heat accumulation (growing degree-days). The general ripening capabilities include hybrid grape varieties through early season, mid-season, and late season ripening V. Vinifera and even table grapes in the warmest areas of Region V. The general wine styles include lighter, more subtle wines with lower alcohol and brighter fruit aromas and flavors (including Champagne and other sparkling wines) found in cooler climates (Regions Ia, Ib, II and lower III) to bolder, bigger wines often with higher alcohol and lush, darker fruit aromas and flavors that are found in warmer climates (Region III, IV and V). Region V was state as also having a tendency to be more suitable to higher production wines, Sherry and other fortified wines.

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