Not just another hot-climate region

“The Texas Hill Country is demanding…but generous”

So goes the motto of Local Customs. It applies to nearly all aspects of grape growing and winemaking, and perhaps the best example comes from understanding heat accumulation in our vineyards. 

One important way we measure the relationship between heat and plant maturity in agriculture is a concept known as Growing Degree Days, or GDD for short. GDD’s are a measure of heat accumulation used to predict plant and insect development rates such as the date that a flower will bloom, an insect will emerge from dormancy, or a crop will reach maturity. For grapevines, an air temperature of 50°F has traditionally been used as the base temperature, as it is the temperature threshold below which grapevines will not grow. The formula for GDD calculates the amount of time in the day where air temperatures exceed this 50 °F threshold and tells us how many hours of grapevine growth & maturity occur during a particular day. 

It’s easy to imagine just how different the GDD measurements of two different winegrowing regions could be, even those growing the same varieties. If you start your annual measurement on January 1st, think about what kind of numbers you would expect to see in the first 3 months of the year for Pinot Noir in Champagne vs Sonoma.

But we’re interested in particularly hot regions, since that’s the viticultural reality for us here in the Texas Hill Country. So, here is a graph showing the GDD accumulation of 5 different wine regions known for their warm climates:

Paso Robles, Ca; Jumilla, Spain; Catania, Italy; Wimberley, Tx'; Beiruit, Lebanon all compared by annual GDD accumulation

There are lots of interesting takeaways here, but I believe the most interesting aspect is the delta between the two hotter and 3 cooler regions during the grape growing season of March-August. Let's put a magnifying glass up to these 6 months and compare specifically Wimberley, Tx and Paso Robles, Ca.

As we can see, these two growing seasons look very different even though they both grow many of the same varieties, namely Mourvedre, Syrah and Grenache. The end of May usually marks the beginning of veraison (fruit-ripening) here in the Hill Country, at which point we have accumulated around 2000 GDD’s - Paso Robles won’t see that figure until mid-August. By then, we have already picked all of our white varieties and most of our reds! 

This is kind of like saying if you’re driving from Austin to Dallas, after 2 hours in the car Paso Robles is in Waco and Wimberley can already see the Dallas skyline. 

So what does this tell us about wine? It tells us that maybe we need a new frame of reference when it comes to assessing fruit maturation. So much of the collective understanding around ripening is tethered to the idea of slow, gentle accumulation of sugars, polyphenols and flavonoids while preserving precious acidity. The relationship between sugar and acid is so complex that it deserves it’s own post, so for now I’ll simply say -  we are clearly operating under an entirely different set of rules here in the Hill Country compared to other hot-climate regions. 

Let me leave you with a metaphor to consider. Berry ripeness has always been considered a gentle process wherein a vine’s ability to slowly develop with long periods of inactivity (temperatures under 50°F) create balance and subtlety. It reminds me of the tedious process it takes to properly bake a croissant or a souffle. But what we experience down here in the Hill Country is more akin to a Neopolitan pizza oven - the extreme temperatures and rapid cook time create a distinct complexity that can’t be achieved any other way. 

If you’re interested in seeing for yourself what kind of unique wine expression comes from the viticultural equivalent of growing grapes in a brick oven, try a bottle of Local Customs Rosé.