The UC Davis Heat Summation Scale is a tool developed by the University of California, Davis to assess the suitability of different grape varietals in California Wine Country. This scale is based on the concept of degree days, which is a measure of accumulated heat over a specific period of time.
To understand the UC Davis Heat Summation Scale, it's important to first grasp the idea of degree days. Degree days are calculated by subtracting a base temperature from the average daily temperature. In this case, the base temperature is 50 degrees Fahrenheit. This calculation is done for each day between April 1st and October 31st, which is considered the growing season in California Wine Country.
The result of this calculation represents the amount of heat that the grape vines are exposed to during the growing season. The UC Davis Heat Summation Scale takes this data and categorizes it into different zones, each indicating the suitability of different grape varietals.
In terms of grape growing, different varietals have different heat requirements. Some varietals thrive in cooler climates, while others require warmer temperatures to fully ripen. The UC Davis Heat Summation Scale helps winegrowers and winemakers identify the most suitable grape varietals for their specific microclimate.
The scale is divided into five zones, ranging from Zone 1, which has the lowest heat accumulation, to Zone 5, which has the highest. Each zone corresponds to a range of degree days, and certain grape varietals are recommended for each zone accordingly.
Zone 1, with the lowest heat accumulation, is suitable for cool-climate varietals like Pinot Noir and Chardonnay. These varietals prefer cooler temperatures and longer growing seasons to develop their unique flavors and characteristics. Zone 2, with slightly higher heat accumulation, is suitable for varietals like Merlot and Sauvignon Blanc.
As you move up the scale, the heat accumulation increases, and varietals like Cabernet Sauvignon and Syrah are recommended for Zone 3. Zone 4 has even higher heat accumulation and is suitable for varietals like Zinfandel and Grenache. Zone 5, with the highest heat accumulation, is suitable for varietals like Mourvèdre and Petite Sirah.
The UC Davis Heat Summation Scale is a valuable tool for grape growers and winemakers in California Wine Country. It helps them make informed decisions about which varietals to plant based on the specific climate and heat accumulation of their vineyard site.
Personally, as a sommelier and brewer, I have seen the impact of climate and heat accumulation on grape varietals and their resulting wines. I recall visiting a winery in California that was located in Zone 4 according to the UC Davis Heat Summation Scale. The winemaker explained how the warm climate in their region allowed them to specialize in bold, full-bodied red wines like Zinfandel.
On the other hand, I have also visited wineries in cooler climates, such as those in Zone 1, where the focus was on delicate, elegant wines like Pinot Noir. The winemakers explained how the lower heat accumulation in their region allowed the grapes to retain higher acidity and develop more nuanced flavors.
The UC Davis Heat Summation Scale is a valuable tool for understanding the heat requirements of different grape varietals in California Wine Country. By categorizing vineyard sites into different zones based on degree days, it helps grape growers and winemakers select the most suitable varietals for their specific microclimate. This scale plays a crucial role in shaping the diverse wine landscape of California.