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Dear Dr. Vinny,

Is there any way to test red wines for possible artificial coloring? We were tasting some Chilean reds and it appears to leave a residual tint on one’s tongue and teeth. Admittedly, they were not high-end labels.

—J.R.E., Capo Beach, Calif.

Dear J.R.,

If you’ve ever been to a large wine tasting, say our Grand Tour, you might start to notice that most everyone in the room has a purple grin. That’s not from food coloring, it’s just a side effect of tasting red wine, which can have quite a bit of pigment in it, and that pigment can stain your tongue and teeth.

Some red grapes—Petite Sirah and Cabernet Sauvignon come to mind—have more pigment than other grapes, and there are practices a winemaker might use to coax more pigment (and flavor) out of a grape. I find it helps to think of grapes like tea bags—the longer they steep, the more color and flavor you’re extracting.

It has nothing to do with a wine being high-end or not, but how much pigment ends up in your mouth has a lot to do with the pH in your saliva and the protein on your tongue. If you haven’t eaten in a while, and if you’re dehydrated, your tongue will be more purple (purpler?) than if you have been drinking water and have recently eaten. You also might like to read my tips for dealing with red-wine teeth.

—Dr. Vinny

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