How much does a glass of wine contain? It may depend on the glass

If you’ve ever wondered how you got tipsy when you only had a glass or two of wine, the answer could be in the sort of glass you used. Drinking from a wide glass is just one way that you might be getting more than you thought.

Unlike a bottle of beer, or a shot of spirits, a glass of wine is rarely an exact measure except in bars or restaurants. Researchers from Iowa State and Cornell universities found there were several conditions that could cause someone to pour with a heavy hand.

“People have trouble assessing volumes,” Laura Smarandescu, coauthor of the research study and an assistant professor of marketing at Iowa State, said in a statement.

Participants in the study – 73 students and staffers who drank at least one glass of wine in a given week -- were asked to pour what they considered a normal glass of wine – the National Institute on Alcohol Abuse and Alcoholism says that’s 5 ounces.

If they were pouring into a wide glass, they poured about 12% more than if they poured into a narrow wine glass. The same was true when people held a glass, rather than pouring into a glass on the table. The researchers tried other conditions, too. People poured 9% more white wine into a glass than red – because of the contrast of color, they said. The food and other things on the table had less effect, the researchers wrote.

Such conditions make it easy to drink more than intended, said another coauthor, Douglas Walker, an assistant professor of marketing at Iowa State. Their research was published this week in the journal Substance Use and Misuse.

If a person thinks about how much wine he drinks based on the number of glasses, that could be a problem, Walker said. “One person’s two is totally different than another person’s two.”

It’s important to become aware of portions – just as people have for food, says coauthor Brian Wansink, director of the Food and Brand Lab at Cornell University. And the participants were asked about the conditions after the pouring; the researchers found they were generally accurate about which conditions had influenced them.

“Increasing awareness of pouring biases is a step toward limiting alcohol intake for improved health outcomes and preventing alcohol-related problems,” the authors wrote.

Mary.MacVean@latimes.com

@mmacvean on Twitter