Chemist Pete Wishnok of the Massachusetts Institute of Technology explains.

The Internet is full of Web sites discussing whether club soda can defeat red wine stains. Some experiments show that club soda does not work very well, whereas others indicate that it is pretty good at removing red wine, so the evidence still seems to be mixed. There's no particularly good chemical reason why club soda should remove stains: it's essentially just water with carbon dioxide dissolved in it, along with some salts. (It is weakly acidic, so it might decolorize stains that can act as acid-base indicators.) Almost everyone, though, seems to have a story.

In my experience, club soda does work sometimes. For instance, it's worked dozens of times for wine spills on our living room carpet (which probably says more about our lifestyle than it does about club soda). But it didn't work at all on the tablecloth during Christmas dinner, even though the laundromat did the trick the next day.

The most common theory suggests that the secret ingredient is the bubbles, and there may be something to that. What's probably more important, however, is a combination of how fast you can run and the nature of the fabric involved. For example, our carpet is a synthetic that absorbs stains slowly so--if you get there quickly with lots of paper towels--the club soda simply acts as a carrier to help blot everything up. Water would probably work as well, but club soda is more fun. In the case of the tablecloth, the club soda might have diluted the red wine out and helped keep it from setting, so that the laundry detergent could finish the job later. But the club soda itself did not do much for the stain other than spread it around.

My conclusion is that if club soda works, plain water probably works as well. Either way, the stain is gone. If it doesn't work, then a commercial stain-removal product might save the day. In addition, a particular commercial stain-remover might work better with a given set of fabrics, so it's a good idea to keep a couple of very different ones under the sink.

Overall, the answer to why club soda works when it works is probably similar to the age-old question of whether hot water freezes faster than cold water. First a nice, controlled experiment is necessary to show that its true, and then a lot more work is required to figure out why. All in all, its probably just as much fun to let go of it scientifically and happily compare your theories with those of your friends over a glass of red wine.

Answer originally posted on February 9, 2004.