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Tapping a beer can is a time-honoured way to stop it fizzing over when you open it, but does it work? Sadly not, according to researchers who carried out a randomised trial to find out.

There is a theoretical rationale for tapping your brew. Bubbles of carbon dioxide form on the inner surface of a shaken can. When it is opened and depressurised, the bubbles swell and rise to the surface, taking precious beer with them.

Tapping the can, some proponents say, dislodges bubbles from the sides of the can, making them rise to the top where they won’t expel beer when the can is opened.


“Being a scientist, I always wanted to know whether it actually has an effect,” says Elizaveta Sopina at the University of Southern Denmark in Odense.

She and her colleagues approached drinks firm Carlsberg to supply beer for the experiment. It provided more than a thousand 330-millilitre cans, but had no involvement in the study design or analysis.

Half of the cans were put on a mechanical shaker for two minutes, with a level of vigour intended to simulate being transported on a bicycle. Half of the cans in the shaken and unshaken groups were “tapped” by flicking them on the side three times.

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The testers who opened the cans didn’t know whether they had been shaken or tapped. The cans were weighed before and after opening to measure how much beer escaped. The unspilt beer didn’t go to waste – it was offered to staff and students at the university, along with snacks.

The shaken cans lost on average 3.45 grams of beer on opening, compared with 0.51 grams for unshaken cans. However, tapping the can didn’t make a significant difference to how much beer was lost.

This suggests that, for beer cans shaken this way, tapping or flicking doesn’t help bubbles rise to the top, Sopina says. That may be because beer contains barley proteins that stabilise bubbles, a process that helps to create the foam head in a glass of beer. These proteins may prevent bubbles from rising to the top of the can. It remains to be seen whether tapping might be helpful for other carbonated drinks.

For beer drinkers anxious to avoid wastage, the best strategy is not to rush things, says Sopina. “If you want to save your beer, let it settle.”

Reference: https://arxiv.org/abs/1912.01999