AMES, Iowa - People who drink wine often don't know how much they are consuming, researchers at Iowa State and Cornell universities found in a new study.
Though the National Institute on Alcohol Abuse and Alcoholism says a standard serving is 5 ounces, varieties of wine glass shapes, sizes and colors make it hard to keep track of just how much goes into a glass.
"We all know that even though we believe we're in control of our own behavior, often cues in the environment influence how we consume," said Laura Smaradescu, an Iowa State marketing professor here and co-author of the study.
The study, published in Substance Use and Misuse, found that participants poured 12% more wine into a wide glass than a narrow one. They also poured 12% more wine into a glass they were holding, compared to one placed on a table.
Color contrast affected pours, too. Participants overpoured white wine into a clear glass by 10%. Less overpouring occurred when the wine was red.
Even after participants were informed of their habits, they still poured more than a serving, Smarandescu said.
"A lot of times consumers don't know how much they drink. Especially when they buy a bottle of wine, it's less clear how much each person consumes," she said. "And when people pour on top of wine still in a glass, that bias increases by a lot."
Even bartenders made the same mistake in a previous study, Smarandescu said. Wider glasses tended to get a bigger pour "because we generally judge volumes by height."
And it's not just wine. Mixed drinks served in pitchers also tend to be overpoured, especially if the drink does not contrast to the color of the glass.
But beer, served in premeasured containers, doesn't pose the same problems for consumers. On the flip side, those cardboard boxes of wine so popular at parties don't even indicate how much has come out of the box.
Wine marketers take advantage of the pouring conundrum by packaging wine in containers that allow for self-pouring and encouraging the use of wider and shorter glasses so people pour more.
For consumers concerned about their alcohol intake or trying to control their weight, knowing how much they drink is pivotal. Smarandescu suggests avoiding wider glasses, and perhaps switching to taller, narrower glasses, which actually help people drink less.
Stick to red wine, and when refilling, put the glass on the table and make sure it's empty first. Most important: Just be aware that over-pouring can and does happen, she said.
"When people are aware of bias, they're likely to adjust behaviors," Smarandescu said.