Rinsing out a used wine glass turns the water blue

[Kent Wang]

When rinsing out a glass of Messina Hof Private Reserve 2001 port wine, the water turns a light blue and stays that color for about fifteen minutes and eventually fades. What is going on? Is this evidence of a dye that's been used? This is hardly a world-class wine, just one from a local Texas winery that I happen to like.

[jsolomon]

There are compounds of different color in wine with differing "strengths" of color. When you have finished with the glass, you may have some that have stuck to the inside of the glass either through their affinity to the glass itself, or something stuck to the glass--detergent, glycerol, etc.

Either the pH of what's on the glass or other parts of its general chemical environment cause the colored molecule that is dissolved in it to change color. Then, when it is back in a mostly water environment, it changes back to its original color. It's nothing to worry about.

Edit because I read the question closer.

Edited January 24, 2006 by jsolomon (log)

[David94928]

When rinsing out a glass of Messina Hof Private Reserve 2001 port wine, the water turns a light blue and stays that color for about fifteen minutes and eventually fades. What is going on? Is this evidence of a dye that's been used? This is hardly a world-class wine, just one from a local Texas winery that I happen to like.

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Red wine pigments are red at a pH of 3-4 (the pH range of wine) but turn almost black when they reach a neutral pH of more like 7. When mixed with a fair amount of water the pigments might look slightly bluish. If you've ever seen the hands of a winemaker during the harvest, they can be so black it looks like the person's been working on a car. This is because the pH of human skin is about 7 or neutral and the grape/wine color pigments turn from red to black.

It's just the natural chemistry of wine and nothing to worry about.

David