Manifesto: The Texas Wine Discussion Starts with Diurnal Temperature Swings, But Goes So Much Further
How many times have you heard winery and/or vineyard reps say, “This vineyard location benefits from warm to hot days that develop strong fruit character, but also have cool nights that helps maintain acidity in the grapes”?
It’s repeated, repeated and repeated. It’s almost like a mantra in most wine regions, particularly in California…but is it true? And, is that really the discussion we need to have?
In most new world wine growing regions, the challenge in grape growing (numero uno) is getting the grapes to physiological (phenolic) ripeness before sugar levels get too high and the acidity starts to drop off and pH starts to shoot up making wines undrinkable and unstable.
But, is the need for large diurnal temperature (i.e. the day-night temperature) swings counter-productive. There is definitely a school of thought (particularly in old world European grape growing) that for flavor development in the grapes, they need uniformly moderate temperatures.
Europe’s best and most widely regarded wine producing regions characteristically have temperatures that vary over narrow ranges, both day-to-night and day-to-day throughout the ripening portion of the growing season. Relatively moderate and constant temperatures during ripening favor certain biochemical processes that define the color, flavor and aroma of wine grapes.
Why is this true? The answer is likely this: biological chemical reactions are driven by enzymes. These enzymes’ activity levels are a function of temperature. So it is likely that the enzymes relating to phenolic development do not work as well in extremes of temperature. But, warmer regions have found a way to handle this problem. It’s blending. In the notably hot Rhone Valley they have up to 13 grape varieties of grapes that can be legally used in a Rhone blended wines; even the noted “lip stinger”, Picpoul Blanc that brings lip smacking crisp acidity to the blend even in the hottest of years.
So, what about vineyards in what are characterized as having hot days like we have in Texas (and particularly this summer) and when night time cooling is low to moderate? In these sites, sugar development and acid drop are likely to outpace phenolic development and structural ripeness. This situation leaves the grape growers with two choices:
- Pick early and have underdeveloped phenolics with accompanying herbaceous or other unattractive flavors (this works surprisingly well for most white grape varieties, less so for reds), or
- Pick later with much higher sugar levels and low acidity that must be dealt with at the winery with strategies designed to moderate alcohol content and increase acidity in the finished wine, but run the risk of bringing undesirable characteristics of their own.
In California, they have high daytime temperature but big day-night temperature swings brought by cool Pacific breezes at night. In contrast, Bordeaux has a climate where the Atlantic moderates both the day and nighttime temperatures and thus more completely minimizes temperature fluctuations. Both regions can grow classic European varieties of grapes (Chardonnay, Sauvignon Blanc, Merlot and Cabernet Sauvignon), but California’s wines tend to be higher in alcohol and lower in acidity than wines made from the same grapes but in Europe.
What about frontiers of the modern wine world like Texas? We have summer daytime temperatures in the mid-90s that can even reach the low 100s by mid-summer, but this is not that much different than in other new world grape growing regions like California (Napa), Washington state (eastern regions) and even Australia. Unfortunately, Texas doesn’t have a large body of cool water to its west that helps dry a diurnal temperature swing.
What we do have in Texas is elevation and dry, arid conditions. As you travel in a northwesterly direction from the eastern Texas Gulf Coast near Houston (45 feet above sea level) the elevation increases to between 1000 to 2000 feet by the time you reach the Texas hill country near Austin, San Antonio and Fredericksburg. If you continue on this northwestern trajectory and eventually find yourself in the region between Lubbock and the New Mexico border (the Texas high plains), you’ll be at 3500 to 4000 feet (that’s a thousand feet higher than the Argentine Mendoza). It’s dry as a bone up there and has lots of red sandy loam to go around.
The net result is that the vineyards in the Texas hill country get moderate night time cooling, probably insufficient for Classic European varietals to be within their usual parameters. However, by the time we reach the Texas high plains, things would be closer to the bar set by California’s wine producing regions, but still not quite there. Consequently, we can grow Cabernet, but it is going to be a good “warm weather” cabernet, not the Napa Valley kind of wine you might expect. Winemakers can make some adjustments if they harvest right and provide judicious treatment of the juice at crush, or use of blending with other grape varieties that have more tolerance to the heat and that preserve their acidity. These are generally grapes that originate from southern regions in Spain, Portugal, southern France, southern Italy, Sicily and Sardinia. A good example of this latter approach is Llano Estacado Winery’s Viviano (made with part Cabernet Sauvignon and part Sangiovese).
For a longer term and more permanent fix, more of these “Mediterranean” grapes need to be planted in Texas. The picture that is becoming evident is that the Texas high plains may be like Spain, southern France and Italy, but the Hill Country may be more like Portugal. However, the grapes selected for these regions need to fit within the other constraints that our continental climate brings. They need to bud late or have prolific secondary buds to beat the late spring freezes (this is the single biggest threat to low harvest yields in Texas) and be able to quickly shut down after harvest to resistant winter kill when the winter cold sets in.
As you can see, the discussion of growing wine grapes in Texas starts with the question of our summer time heat and the discussion of diurnal temperature variation, but gets even more complex. However, this is precisely the discussion that we need to have.
Texas just ain’t Bordeaux, and it ain’t even Napa Valley no matter how you slice it or dice it. It’s time to get real and move on to discover what the Texas wine experience really will be and set our vision toward how to reach 10,000 acres of wine grapes and how to get there a quickly as possible. Only once we get to that point, will the global wine world take up as a serious player.
Russ, isn’t this the reason the state needs to do research in grape growing, just like it does for other agricultural products? Except, of course, that the state doesn’t consider grapes to be an agricultural product and has cut its research funding.
In general you are correct. But, please note that we did score a big win with some emergency funding (see: https://vintagetexas.com/?p=5124)….The Association (Texas Wine and Grape Growers Association – TWGGA) has just been notified formally that Commissioner Todd Staples has decided to address what many in the TWGGA leadership have indicated is the industry’s top priority. Commissioner Staples has decided to invest $200,000 to continue the viticulture education program administered by Texas AgriLife Extension.
Jeff and Russ,
Please note that TAMU has established several research vineyards to try to find the best varieties for different areas of the state. Here in the Gulf Coast region we have one in Industry, near Brenham, with about 30 different varieties in a test vineyard. This includes not only experimental specimens of PD-resistant vinifera but new and unusual varieties that may have some potential for the wine industry.
I agree, Russ, that we need more grapes. Legislation that would make it less cost effective to purchase cheap California Central Valley fruit would help drive Texas vineyards forward and increase acreage.