Wine Importing and Marketing Services

Just How Important Is Diurnal Shift to Wine?

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If you’ve ever encountered the word “diurnal” it was likely during a visit to a California winery or between sips at a winemaker dinner. And then you probably heard it again at the next place you visited and the one after that and so on. Diurnal means “daily,” and in winegrowing regions “diurnal swing” or “diurnal shift” is the difference between the maximum daily temperature and the minimum nightly temperature in a 24-hour period. It is a valid metric for understanding certain aspects of grape and wine quality, but only—in my view—when used in moderation. Some wine producers, eager to convince you that their vineyards—and not the vineyards of their colleagues in other Golden State counties—are especially blessed, are using it in immoderate ways.

Lake County has diurnal swings that other regions can’t duplicate,” boasts Lake County Winegrowers on its website. The swing can be more than 50 degrees and helps produce more complex flavors and balance in both grapes and wine, according to the article. But it seems that other regions can duplicate Lake County’s diurnal swing. In Paso Robles, 300 miles south, winemakers also cite a difference of 50 degrees or more in a day. Paso Robles Wine Country Alliance claims its diurnal shift is “a greater day-to-night temperature swing than any other appellation in California.”

I am a fan of both Paso Robles and Lake County wines, but are claims like these helpful when you’re shopping for wine?

Let’s take a deeper look: Wine grapes gradually develop sugar, which is fundamental for alcohol and fruit flavors, in the heat and sunshine of summer days. Natural fruit acid in the grapes moves in the opposite direction. It starts high and slowly decreases until harvest.

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