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beer-headEver wondered why foam comes up when you are pouring yourself that drink. Probably not. But if it has crossed your mind then Scientist at Universidad Carlos III de Madrid (UC3M) have the answer.

Apparently there is a whole process involve:

“A sudden vertical impact on the mouth of a beer bottle generates a compression wave that propagates through the glass towards the bottom. When this wave reaches the base of the bottle, it is transmitted to the liquid as an expansion wave that travels to free surface, where it bounces back as a compression wave. This train of expansion-compression waves drives the forced cavitation of existing air pockets, leading to their violent collapse. A cloud of very small daughter bubbles are generated upon these collapses, that expand much faster than their mothers due to their smaller size. These rapidly growing bubble clusters effectively act as buoyancy sources, what leads to the formation of bubble-laden plumes whose void fraction increases quickly by several orders of magnitude, eventually turning most of the liquid into foam.” (source http://arxiv.org/abs/1310.3747)

So there you have it. Next time you’re out for a drink dazzle your drinking buddies with you scientific knowledge on beer.