Monday September 3 2012
A curved glass can make it more difficult to judge volume
“Using a curved glass could get you drunk quicker, scientists say,” The Sun has reported.
The news comes after researchers found that, on average, people drank alcohol more quickly from a curvy glass, compared with a straight one. This experimental study aimed to look at the influence of two factors on how quickly people drank – the type of drink and the type of glass used. Participants took about four minutes longer to drink the same volume of alcohol from a straight glass compared with a curved glass.
The researchers argue that there is a possible connection between drinking speed and the ability to estimate accurately the halfway point of a glass. They suggest that it is easier to estimate volumes in a straight glass so people can judge more accurately how much they have drunk. The researchers argue that because judging the halfway mark in a curved glass is trickier, drinkers underestimate how much they have drunk, causing them to drink at a faster rate.
Interestingly, there were no differences in drinking speed when a non-alcoholic soft drink was drunk. The researchers speculate that people may subconsciously monitor how much alcohol they are drinking so they do not get too intoxicated.
These findings merit further study. As the researchers suggest, manufacturers of curved beer glasses may want to put a halfway marker on the glass to aid sensible drinking.
Where did the story come from?
The study was carried out by researchers from the University of Bristol and was funded by an Alcohol Education and Research grant.
The study was published in the peer-reviewed medical journal PLOS One.
The findings of the research were generally accurately reported by the media. However, the headline claims by both The Sun and Metro – that curved glasses ‘get you drunk quicker’ – are slightly wide of the mark. The study has not examined whether drinking slightly more quickly from a curved glass makes you drink more alcohol overall, and has not examined whether participants became drunk. How quickly you get drunk depends on a wide range of variables, not simply how quickly you drink.
To find out more about the media’s recent relationship with alcohol, read our special report: What’s your poison? A sober analysis of alcohol and health in the media.
What kind of research was this?
Increased alcohol consumption is known to be associated with the risk of several chronic diseases such as liver disease, heart disease and some types of cancer. Rates of excess alcohol consumption and binge drinking among teenagers and young adults in the UK are known to be high.
Several public health strategies have considered ways to try to reduce consumption, such as increased taxation (such as a “unit tax”) and reduced opening hours for pubs and off-licences. But due to the lack of both political and public support it is unlikely that these types of strategies are going to become law in the near future.
So the researchers were looking to see if there were more subtle methods that could be used to reduce alcohol consumption – namely whether the shape of the glass used influences how quickly people drink.
The study involved participation in two experimental sessions, approximately one week apart. The study was relatively small and the results would need replication in larger population groups before it could better inform public health policy.
What did the research involve?
The study recruited 159 social alcohol drinkers (reported to drink between 10 and 50 units a week for men and between five and 35 units a week for women) from the University of Bristol and the local population. All participants were in good mental and physical health, with no reported history of alcohol dependency, and had to have abstained from alcohol for 12 hours prior to each test session.
There was an even split of men and women in the study and the average age was 23 years.
The study involved two glasses of equal volume (12fl oz or just under 355ml) but different shape:
- the first was a straight-sided glass with a reportedly clear midpoint (the halfway point in terms of height and volume was the same)
- the second was a curved flute-style glass with an ambiguous midpoint (the midpoint in terms of height and volume was not the same)
On two separate occasions participants were randomly assigned to drink either an alcoholic drink (lager with 4% alcohol volume) or a non-alcoholic drink (such as 7UP) from the straight or curved glass, and told to drink it at their own pace while they watched a nature documentary. Their drinking time was recorded by video and analysed. The main outcome of interest was total drinking time. Other outcomes assessed were total number of sips, interval between sips and sip duration.
The participants also completed a computerised task to judge the midpoint of the glass. A sequence of 61 photographs with liquid volumes ranging from empty to full were presented and the participants had to judge whether the picture represented more or less than half full, recording their judgement on a keypad.
The participants were reported to be unaware of the study’s intent, and to disguise this they were asked to complete other unrelated tasks, including rating their liking of the beverage and their perception of its alcohol content. They were also asked to complete a wordsearch. This was because researchers were concerned that if the participants were aware of the true purpose of the study it could influence how quickly they drank.
What were the basic results?
In general, drinking times were longer with the alcoholic drinks than with the soft drinks. Participants took longest to drink the alcoholic drink from the straight glass. Participants took about four minutes longer to drink alcohol from the straight glass compared with the curved glass (about 60% slower). They took more sips and longer time between sips with the straight glass. Conversely, there was no difference in the time it took to drink a soft drink from the straight or curved glass.
They found that when participants judged the volume of liquid in the glasses they tended to think the halfway point was lower than it actually was for both the straight and curved glasses. However, when they compared responses for the two glasses, they found that volume perception was more impaired for the curved glass than for the straight glass.
This would suggest that most people have a tendency to underestimate how much alcohol they have drunk.
How did the researchers interpret the results?
The researchers conclude “glass shape appears to influence the rate of drinking of alcoholic beverages. This may represent a modifiable target for public health interventions”.
This experimental study found that people took longer to drink the same volume of alcohol when it was presented in a straight glass compared with a curved glass. A difference in drinking time was not observed when it was a soft drink.
This study will be of public health interest and may suggest another possible way to tackle the UK’s excess alcohol and binge drinking culture. Arguably, placing a halfway line on the curvy type of glasses (which are often used for branding by the larger drink manufactuers) could lead to slower drinking times.
However, the findings will need replication in further studies and the study did have a number of limitations.
- This single study included 159 participants, predominantly university students. It may not be representative of other age groups (though it is true that high levels of drinking are often observed among teenagers and young adults and so this is an important group of interest). Also, people who took part in the study had no (reported) history of alcohol dependency, so the findings may not apply to people who do have a problem with alcohol.
- There is the possibility that this experimental scenario of sitting alone watching a documentary may not be entirely representative of a real-life social drinking situation (such as drinking in a pub).
- We do not know that the increase in drinking speed with a curved glass would necessarily relate to an increase in the total number of alcoholic drinks consumed (for example, on a single drinking occasion people may pace themselves according to a total number of pints).
Also, the study cannot assess the influence of other things that may influence drinking speed, such as:
- when drinks are given in a bottle rather than a glass
- the type of alcohol (such as a glass of wine or spirits rather than a glass of lager)
- whether different types of curved glasses on the market compared with the one used in this study may influence drinking speed
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter.