(CBS) Want to drink only one glass of wine? You may want to pay special attention to your glass. How much alcohol actually goes into that pour may depend on the shape of the glass and whether you're holding it, new research finds.
A Sept. study published in Substance Use and Misuse showed that subjects who were told to pour an average wine glass varied in their judgments depending on different environmental factors that were present.
"People have trouble assessing volumes," co-author Laura Smarandescu, assistant professor of marketing at Iowa State, said in a press release. "They tend to focus more on the vertical than the horizontal measures. That's why people tend to drink less when they drink from a narrow glass, because they think they're drinking more."
Wine pours are especially hard to judge because unlike hard alcohol that is served in a shot glass or bottled beverages, there is a lot of room for interpretation. A standard glass of wine is supposed to be only five ounces, according to the National Institute on Alcohol Abuse and Alcoholism.
The researchers asked 73 subjects who drank at least one glass of wine a week to pour what they considered to be a normal wine glass.
If subjects were pouring wine into a wide glass, they poured about 12 percent more than when they were pouring it into a narrow glass. They also poured 12 percent more wine if they were holding the glass, compared to when it was set on a table.
The contrast between the wine color and the glass also played a role. People poured 9 percent more white wine in a glass than red.
The size of the table and whether or not there were food and other items on it did not make a difference in the pours.
"If you ask someone how much they drink and they report it in a number of servings, for a self-pour that's just not telling the whole story. One person's two is totally different than another person's two," study co-author Douglas Walker, an assistant professor of marketing at Iowa State, said in the press release. "Participants in the study were asked to pour the same amount at each setting, but they just couldn't tell the difference."
A previous study also showed that the shape of a glass may affect how fast a person chugs a beer. People tended to drink slower if their beer was served in a straight glass instead of a curved one.
The researchers said that if people want to ensure they aren't drinking a lot, they should use smaller white wine glasses and only pour a drink when it is on the table. They also called for more public education on how much a proper serving of alcohol should be.
"I think this helps us understand drinking behaviors to see how these cues influence individual pours. When you add this information about how people pour, to survey data of how much people drink, then you have a more complete picture about how people drink," Smarandescu said.
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