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K, but how do you do this? How do you make sure that your beer doesn’t overflow, but the other person’s does?
The trick is in the hit, the sliding bottles against one another is misdirection. If you hit an open beer bottle on top another open beer bottle the bottom one will froth up and the top will not. I believe this is due to the pressure created but I’m not 100% sure. In the video the first person hits very lightly the second hits harder
Yes it is the pressure, but not in the way you may think. The key is to hit the bottle just hard enough to accelerate it slightly faster than the speed of gravity. This causes the bottom of the bottle to separate from the beer inside and creates a small area of extremely low pressure between the bottom of the bottle and the beer. Of course, this collapses shortly after the initial impact, which sends a shockwave through the beer. This in turn releases the dissolved gases which then causes the foam.
The real fun part is when you hit it too hard and the force with which the beer hits the bottom of the bottle actually blows it out.
It actually took me 3 times before I learned to not blow out the bottle's bottom...