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Author Topic: Why does sticking my finger in the flow stop soda from overflowing?  (Read 6917 times)

Steven King

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Steven King asked the Naked Scientists:
Hello scientists!

I love the show and came up with this question today when pouring a can of soda into a cup.  

Sometimes when pouring, usually when slightly warm soda into a cup of ice, the foam expands quickly and threatens to overflow.   I have found over the years, that if I stick my finger into the advancing foam, it will cause the foam to pop/diminish quickly and keep the foam from overflowing.  

So my question(s) are, why does this work in dissipating the foam quickly, why doesn't it work all the time, and what could I do to make it work all the time?

Thank you so much for making a wonderful podcast!

Steven King

What do you think?


Offline Bored chemist

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I don't know about this trick (Though I might remember if for the future) but I know that you can destroy the head on beer if you have fat or oil on your lips when you take a drink.
Perhaps this is the same sort of thing.

Offline Chemistry4me

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Offline mad scientist

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The sebum on your skin contains fatty acids which are an excellent defoamer.
Next time pouring a beeer, rub your finger on the skin beside your nose where most people's skin is especially oily.
Stick that finger on the foam generated and it very rapidly disappears.
When yu are at a pub watch the bartender when they are pouring yu a beer to make sure they are not adding their skin sebum to your head of beer.

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