Do California winemakers ever add sugar to their wine? Is that legal?

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Dear Dr. Vinny,
Do California winemakers ever add sugar to their wine? Is that legal?
—Hugh, Susanville, Calif.
Dear Hugh,
The process of adding sugar to must (unfermented grape juice), is known as chaptalization. Even though it sounds like something a winemaker might do to make a wine sweeter, the purpose is actually to facilitate the fermentation process, to make sure there’s enough sugar for the yeast to convert into alcohol. That’s why the sugar is added before fermentation, not afterward.
It’s illegal to chaptalize in California, but cooler regions in the U.S. and Europe, like New York, Oregon, Bordeaux, and Burgundy can allow it, and it can come in handy in a cool year when the grapes don’t get as ripe as they would to easily make wine. In Champagne, chaptalization is not only legal, but many consider it essential.
California vintners are allowed to add grape concentrate, and some feel that can both tame aggressive acidity and make a wine’s body lusher and fuller.
—Dr. Vinny