It's an automatic reflex for many of us: obediently tapping a few times on a can of beer or soda to stop it from frothing over.
The team from the University of Southern Denmark in Odense conducted a randomized test using 1,000 330-milliliter (11-ounce) cans of beer. The cans were placed into one of four groups -- unshaken/untapped, unshaken/tapped, shaken/untapped and shaken/tapped.
The beers were shaken for two minutes using a machine that was set to simulate the effect of riding a bicycle for 10 minutes, a popular Danish method of transporting beer.
The cans were hit three times on the side and opened after roughly a minute, with the teams weighing them before and after opening to find the mass and assess the level of beer loss.
The scientists chose to tap on the side of the can rather than on the top, because it acts on a larger surface area.
The study found "no evidence to support the hypothesised beer-saving effect of tapping," the researchers concluded, adding that the only apparent way to avoid a beer-frothing incident was to wait for bubbles to settle before opening the can.
"The idea came from as a teenager opening can of soda and later beer," Elizaveta Sopina, the lead researcher on the study, told CNN. "It's just what people do. I did it, and then I started to question whether it was actually true and effective or not.
"I was surprised, but not disappointed ... it's good to be evidence-based in your behavior."
Sopina, who is doing a post-doctorate in health economics, gathered an intrepid group of scientists from the university's PhD association to help her conduct the experiment in her spare time.
The 33-year-old from New Zealand said one reason for the tapping not being effective could be because it only affects the bubbles lodged on the inside of the can surface, and not those suspended in the beer.
The researchers noted that the study could be of social value in reducing wrist and finger injuries from tapping, and in reducing excessive beer consumption by forcing drinkers to wait before consuming their beverage. It also improves efficiency for cash-strapped students.
"Our study suggests that one whole can of beer can be preserved by allowing approximately 100 shaken cans to settle," said the researchers. "Post-secondary students, economists and other frugal beer enthusiasts are likely to find satisfaction in this fact. "
Sopina approached Carlsberg to donate 1,000 cans, but said the company had no vested interest in the outcome and were not involved in any part of the study. The opened beers were handed out afterward to "volunteer drinkers," who were mostly students.
Sopina said there had been "a little bit of disbelief from people who practice tapping and flicking," but "this will most definitely not put me off beer."
She added: "I look forward to applying evidence in my future beer consumption. And I think the beer-loving Danes will just need to exercise patience and let the bubbles settle before cracking a cold one open."
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