Today in “Obscure Wine Words,” we’re going to discuss diurnal range. Sounds sort of like a bladder condition, doesn’t it?
But no, the term actually has to do with the climate in winegrowing regions. You might hear it bandied about over the course of a vineyard tour, or in a tasting room while someone is explaining growing conditions and their impact on the flavor and balance of a particular wine.
The term diurnal range is actually used as shorthand for diurnal temperature range. Diurnal comes from the Latin dies, meaning “day.” The word diurnal means a daily cycle. Here, the range means the variation between the hottest and coldest temperatures in a day. Diurnal range can vary from region to region, vineyard to vineyard and even block to block. In a place with some temperature extremes like New Zealand’s Central Otago, the diurnal range can be as much as 60 degrees Fahrenheit, while the range in a more mild region like Napa’s Los Carneros tends to be closer to 30 degrees.
Why does this matter to grape growers and winemakers? The diurnal temperature range of a growing region has an outsize impact on the development of the grapes. Those daily highs mean that sugars will develop in the grape, and that’s what’s turned into alcohol via fermentation. Meanwhile, a significant drop in temperature each day means that the natural acids in those grapes are also preserved.
So when it’s finally time to make wine from those grapes, you’ve got a good concentration of sugar from which to create alcohol, but acidity as well that keeps the wine balanced and tasting fresh.
While overall climate, soil types, growing conditions and more all contribute to the growth of a grape before it is harvested and made into wine, diurnal range is another extremely significant factor contributing to how that grape will develop. But it’s also just a fancy way of saying the temperature variation. Now you know why it’s important, though!
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