Why do I get a foam forming on my glass of squash, but not just a glass of water? i.e. If I fill a glass with water from the tap, with the water flowing pretty fast, there are only a very few, quite large, bubbles which form on the surface of the water, and they quickly dissipate away. If I add a small amount of squash (cordial) to the bottom of the glass and then add the water in the same way, a large number of small bubbles (a foam, I suppose) forms on the surface, and takes 3 or 4 seconds to disappear. Anyone know what's responsible for the difference? It seems related to a soap foam, but I wouldn't have thought there any any ingredients in common.... Cheers!