To test the hypothesis, she and her colleagues randomly divided 160 young, healthy people -- students and faculty members of the University of Bristol, as well as some members of the general public -- into eight groups. It wasn't difficult to recruit participants, Attwood says. "People tend to be quite happy to get free lemonade or beer." Using the standard WHO test for hazardous drinking, called AUDIT, the researchers screened the participants to include only "social beer drinkers," not alcoholics. They assigned each group to drink either about 177 milliliters or about 354 milliliters of lager or soft drink from straight or curved glasses. While the participants drank, they watched a nature documentary deemed emotionally neutral, so that they wouldn't be "sitting there with nothing to do but drink," Attwood says. The team videotaped the drinkers over two sessions, disguising the real purpose of the test with a fake word search task at the end of each session.
After watching video of both sessions and recording how much time it took for the drinkers to finish their beer or sodas, Attwood's team found that one group consistently drank much faster than the others: the group drinking a full glass of lager out of curved flute glasses. In a paper published this month in PLoS ONE, the team reports that whereas the group with straight glasses nursed their 354 milliliters of lager for about 13 minutes, the group with the same amount of beer served in curved glasses finished in less than 8 minutes, drinking alcohol almost as quickly as the soda-drinkers guzzled their pop. However, the researchers observed no differences between people drinking 177 milliliters of beer out of straight versus fluted glasses.
Attwood believes that the reason for the increase in speed is that the halfway point in a curved glass is ambiguous. Social beer drinkers, she says, naturally tend to pace themselves when drinking alcohol, judging their speed by how fast they reach half-full. Another experiment in which participants were asked to judge different levels of fluid in photographs of straight and curved glasses showed that people consistently misjudge the volume in fluted glasses, Attwood says. A simple solution to this problem would be to mark beer glasses with the accurate halfway point, she says. "We can't tell people not to drink, but we can give them a little more control."