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Dear Dr. Vinny,
When you look at a grape, there is sometimes a powdery film covering the skin. Is this dust, or a product of the grape? And does it have any effect on the juice and the wine produced from it?
—Greg C., Danville, Calif.
That bluish or grayish white stuff is called "bloom." You'll find it on grapes, blueberries, plums and other soft fruits. It's a waxy covering that protects fruit from environmental damage like water loss and spore penetration. It is flavorless and doesn't have any effect on juice or wine.
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