The buildup of
foam on a
soft drink (or
beer, for that matter) is a problem that has
plagued man since the invention of
carbonation in drinks. Or at least it's plagued
me, for as long as I can remember. As it turns out, there are a lot of different proposed methods for getting rid of that
head. The first is simply to stop it before it starts, by the way you pour a soft drink. The proper way to pour your carbonated
beverage without getting too much foam is to tilt the cup (or the bottle or spout) so that the drink hits the side instead of
splashing into the rest of the liquid. One might think that this works by
minimizing the
agitation that the pouring causes, thereby lessening the amount of carbon dioxide released, but the truth seems to be that pouring onto the side creates a wider
surface area for the gas to escape from, which reduces buildup (thanks
Geez). Pouring in moderation using this method can actually make foam
buildup almost non-existent after a full cup has been poured. Take a look at
How to pour a beer for more info on this topic. It saddens me to look back and realize how long I went through life without realizing this simple method. Of course it does have its limitations. First of all, you have to be pouring something, so it doesn't necessarily apply to foam buildup in
cans or
bottles being opened. Secondly, it necessitates the need for two hands when one would ordinarily do.
However, there is another tried and proven method for quickly reducing foam in your beverage: the finger method. Simply put, placing your finger in a drink you pour or into the built up foam on a cup will cause the foam to dissipate almost immediately, or keep it from even appearing. The reason behind this seems to be that the natural oils on the skin of your finger create an non-uniform surface on the bubbles, which cause them to burst. Since the oils then have nowhere to go but down and outwards, it creates a cascading effect that pops most of the bubbles above the drink.
Finally, it's widely believed that tapping the side or top of a soda can before opening it will dislodge extra bubbles within, allowing less fizz to form when the can is finally opened, but sources say that's a myth. Tapping any part of the soda can isn't going to do anything to re-mix the released carbon into the liquid, so the whole thing's a worthless endeavor.
Of course, the tried and true method for reducing the head on a carbonated drink is simply to let it sit for a while. Sometimes, it's the only real course of action that one can take to get rid of that foam. It's really not that inconvenient...
EDIT:
hapax says re Getting rid of the foam on a soft drink : A trick I learned in high school -- a shot of diet pop in your regular pop will lessen the fizz considerably. I can't stand the taste of aspartame, but just a splash is enough to do it and doesn't taste too bad. This is easiest to do at those rows of taps in fast-food restaurants. (note: hapax absolves himself of all legal liability should said method fail. -ed)
Sources:
http://www.madsci.org/posts/archives/sep99/938631525.Ch.r.html
http://www.snopes.com/science/sodacan.htm