Heat Summation Regions

Definition - What does Heat Summation Regions mean?

The relative term related to heat summation regions is the "Winkler Scale", named after Albert J. Winkler, a famous horticulturalist, professor and chairman of the Department of Viticulture and Enology from the years of 1935 to 1957. He created the heat summation method along with Maynard Amerine, a system that separates geographical regions and classifies them into five categories based on temperatures during the months of April through the end of October, the growing season for grape vines; regions are named on a scale of 1 through 5 (I to V).

The Five Geographical Regions Are:

  • Region I: = 2,500 degree days
  • Region II: 2,501 - 3,000 degree days
  • Region III: 3,001 - 3,500 degree days
  • Region IV: 3,501 - 4,000 degree days
  • Region V: = 4,000 degree days

WineFrog explains Heat Summation Regions

The basis of the heat summation regions system is that grapevines are not able to grow at temperatures below 50°F (10°C). The days in any given growing region within the dates from April 1 to October 31, are given "degree days". It is measured when the average temperature during the day exceeds the temperature above 50°F. Each degree over 50°F is one degree day. For the Celsius scale, these "days" are converted by multiplying every degree over 10°C by 1.8.

Today, the heat summation regions scale is used in California, Washington and Oregon. It is also being implemented in other states that are growing wine regions.

While the scale is important for dividing the wine regions, it is most important for vintners and winemakers who wish to determine which varieties of wine grapes thrive in each. To give a general idea of which classified region is related to commonly known regions of the world, here are some examples:

  • Region I: The coolest of the regions; Champagne, Willamette Valley
  • Region II: Bordeaux, some of New Zealand, Southern Chile
  • Region III: Rhone, Provence, Tuscany, Catalonia, Napa, Mendoza
  • Region IV: Mendocino, Sonoma, Douro, Dao
  • Region V: San Joaquin Valley, Central Valley, Hunter Valley
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