Why does the head on a soft drink collapse faster if you touch it?



If you pour a soft drink over ice (Coke or Pepsi seems to work best), the head that forms will go down on its own, but if you touch it with your fingertip, even on the edge, the whole thing collapses much faster. I’m fairly certain it has nothing to do with oil from my finger. So what causes the foam to dissipate so much faster?

In: Chemistry

The natural salt and oil on your finger breaks the surface tension of the bubbles and makes them easier to pop, that salt and oil then mixes with the liquid that made that bubble and now touches more bubbles, which does the same to them, causing a chain reaction of collapse.

It’s the oil from your finger. If you don’t believe that, eat some chips or rub the side of your nose to get your finger more oily and try it.

Oil is the enemy of bubbles. The oil film spreads out a LOT and messes up the water surface tension so it can’t form bubbles.