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Dear Dr. Vinny,

Is there any change that can be made in viticulture practices to produce low-alcohol wines apart from using reverse osmosis?

—Ananda K., United Arab Emirates

Dear Ananda,

Oh my, yes! I’ve covered before how alcohol content can vary from year to year, as well as what reverse osmosis is, for those who aren’t already familiar with it.

Keep in mind that alcohol levels in wine are directly related to how ripe the grapes get. Fermentation converts the grape sugars into alcohol, so the more sugar, the more alcohol. Probably the biggest decision a grower makes every year is when to pick, which will be the major factor affecting the ripeness of the grapes. Want lower-alcohol wines? Pick sooner rather than later.

But it’s a little more complicated than that, as Roger Boulton, a professor in the Dept. of Viticulture and Enology at the University of California at Davis, reminded me. Grapes will eventually reach a point of saturation in sugar content where they can’t accumulate any more sugar, but the issue of dehydration can move the needle further. According to Boulton, things like irrigation, rainfall, and even the ratio of root size (which increases water uptake) and leaf area (which affects water loss) all play into the sugar levels of the grapes, and therefore the amount of alcohol in the wine.

—Dr. Vinny

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