Thoughts on Vine Metabolism in Texas
In one of Stephen Hawking’s books, the renowned scientist, warns the reader about his disregarding the advice of the editor who said he would lose half of the potential readers for every mathematical equation he put in the book. He said he had to include Einstein’s famous relation between energy, mass and the speed of light if he wanted to explain the fundamentals of the universe in simple words. I just remember this because in a more human scale matter I’m going to take the risk of losing half of the readers by going a bit deeper in trying to explain why is it that we are able to make such high quality wines at FALL CREEK Vineyards in Texas. So, here we go!
Vitis vinifera (which includes practically all European varieties, though originally from the Middle East), or just vines for our purpose, has two kinds of metabolisms as most of other plants do, the primary and the secondary. The first includes, but is not limited to, the production of metabolites that are essential to plant growth and development, like rich fuel molecules such as starch or glucose, structural molecules such as cellulose and other important molecules found in all plants. On the other hand, secondary metabolites are often colored or fragrant or flavorful compounds and they mediate the interaction of the plant and the environment, including other organisms and abiotic factors like temperature or light.
Among secondary metabolites are polyphenols which include anthocyanin, flavonols and tannins, three of the most important contributors to wine organoleptic properties. Their function within the plant is more or less studied, but the one thing that has been proven is vines growing in ideal conditions of water, nutrients, temperature, light and absence of other pathogens tend to accumulate less concentrations of polyphenols, so, their synthesis is encouraged by the influence of one or more “stress conditions”, in fact, vines show a different response if they are exposed to one stress or to two of them, as it normally happens in nature, heat and drought being the typical example.
The response to stress, particularly heat, not only includes polyphenols but also certain proteins called Heat Shock Proteins (HSP) of several size and functions. Amazingly enough, inside the cells they are able to chaperone (they are actually called molecular chaperones!) other proteins and prevent them from getting affected by high temperature. They act by responding, maintaining and repairing the effects of a heat period, which we know in Texas can be quite extended, and their effectiveness can be seen on this fine looking plant growing under the Texas Hill Country weather.
Where am I going with all this? Well, these molecules are costly for the vine. That’s why they save the effort if they are not needed. They consume significant amounts of energy and resources, so, if put under extreme stress plants may have a different compound composition when compared to plants under normal conditions.
In Texas we have the kind of summer temperatures than can fall into the extreme category, to say the least. Several weeks in a row with maximum temperatures above 95ºF (35ºC), some periods above 100ºF (38ºC) and even a few times above 105ºF (41ºC) would definitely count for the typical condition in central Texas. Also, not to mention, minimum temperatures averaging 75ºF (24ºC) over the same period, though less scarce, contribute to what is usually considered normal.
These summer temperatures do trigger the synthesis of secondary metabolites, like polyphenols and HSPs in particular, all of them, as pointed above, to the expense of energy or, in other words, sugars. The result is a lower sugar/secondary metabolites ratio. Translated into English, this means more ripeness at a particular level of sugar content. For those of you patient enough, an example: imagine two Cabernet Sauvignon plants, one grown in Texas and one in any other cooler region, both with the same sugar content. What this means is that the Texas plant is going to have a more advanced ripeness because it has been spending energy doing things the cooler region plant has not had the need to do.
This did not occur to me immediately. I have been observing this phenomenon the past two vintages since becoming Director of Winemaking at Fall Creek Vineyards in Texas. During the last harvest, I found these fully matured seeds whose grapes were only some 22.6º brix. Consequently, all of our grapes were harvested between 23 and 24º brix with great results. Usually, at that sugar level, grapes are unripe in cooler regions.
I know I must have scared half of you off at the second or third paragraph, and maybe the other half before this last paragraph, but I have this problem of experience telling incontinency, and I had to share these thoughts with y’all!
Sergio Cuadra, Director of Winemaking
References: Al-Whaibi, M.H. 2011. Plant heat-shock proteins: a mini review. J. King Saud Univ. Science 23:139-150.
Downey, M.O, N.K. Dokoozlian, and M.P. Krstic. 2006. Cultural Practice and Environmental Impacts on the Flavonoids Composition of Grapes and Wine: A Review of Recent Research. Am. J. Enol. Vitic. 57:3 257-268.
Morrel, A, M., R.L. Wample, G.I. Mink, and M.S.B. Ku. 1997. Heat Shock Protein Expression in Leaves of Cabernet Sauvignon. Am. J. Enol. Vitic. 48:4 459-464