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What's in a Glass? Study Shows Wine Drinkers Fail to Gauge Serving Size

A study concludes that glass shape and other factors cloud judgment in determining what's a single serving

Ben O'Donnell
Posted: October 8, 2013

With an ever-growing arsenal of flutes, snifters, goblets, copitas and glasses tailored to every region and variety under the sun, you could be forgiven for losing track of just how much wine a glass of wine contains. A new study confirms you wouldn't be alone: Wine drinkers routinely pour different amounts of wine based on the glass. The study also identifies which situations put wine drinkers at risk of unintentionally "overpouring" a single serving.

For the study, published in the journal Substance Use & Misuse, Doug Walker and Laura Smarandescu of Iowa State University and Brian Wansink of Cornell University recorded 73 wine-drinking subjects pouring themselves a glass of wine. Or rather, 504 glasses of wine: The researchers wanted to test whether subjects poured more into a larger glass or a wider glass compared to a more "standard" glass; poured more red wine versus white; poured more while holding the glass or with the glass on a table; and poured differently with a small place setting, large place setting or no place setting at the table. They then quizzed the participants on whether these factors might have caused them to overpour.

The Alcohol, Tobacco, Tax and Trade Bureau (TTB) defines a single serving of wine as 5 fluid ounces. But can drinkers, even experienced ones, really gauge how much wine that represents? "I was looking at two glasses just yesterday, my glass of water and my glass of wine, and they all have different shapes, and it's very difficult," Smarandescu told Wine Spectator. "I was honestly thinking, how much more do I have in this glass versus this glass?"

Her team's research indicates she's not the only one. The average pour into a wide glass was 11.9 percent higher than into a standard one. Subjects holding the glass poured 12.2 percent more than when the glass was placed on a table. White wine pours were 9.2 percent more generous than red. And subjects correctly guessed which factors might skew their judgment. The presence of place settings and the "large" rather than "wide" glass did not significantly affect pour sizes. (Smarandescu hypothesized that if there were food on the table, place setting results might have been different.)

Citing earlier research, the study explains the psychology behind these cues. "When estimating volume, people tend to place a larger emphasis on container height than on its width," so wide glasses get inordinately larger pours. "When standing, it is easier to pour into a glass that is being held than in a glass that is placed on the table," and so participants poured more.

And then there's a phenomenon called Delboeuf’s Illusion that causes people to consume more food or drink if it has a lower color contrast with the container it is served in; because white wine is closer to transparent glass than red, subjects poured more.

In May, after a decade of pressure, the TTB issued a ruling that would allow producers of alcoholic beverages to state Serving Facts on their labels: size per serving, number of servings per container and alcohol content per serving, as well as some nutritional information. Small wineries fear that this voluntary measure, costly for small producers, will lead to a mandatory one. But proponents argue that drinkers have a poorer grasp of serving sizes than they think. The new study supports that argument.

"I think it would be helpful to inform people. It seems like there isn't enough knowledge of what is a standard serving, so I think people attempt to count their drinks to make sure they don't get into trouble," said Smarandescu. "But with things like wine pours it becomes more difficult. So I think it would help to know how many servings are in a bottle."

The study cites previous research that shows bartenders who are made aware of their overpouring still overpour, albeit less. The subjects of this study, though they recognized after the fact when they might have overpoured, still did so. "If participants were trying to be accurate in each pour, they were not, and also post hoc they proved to be aware of the fact that they were inaccurate," wrote the authors.

Were the participants still unable to gauge the correct pour size—or did they simply not care? Smarandescu felt it was the former: "I think people cannot tell."

Trey Rolofson
Colorado —  October 8, 2013 3:45pm ET
Dennis D Bishop
Southeast Michigan, USA —  October 9, 2013 1:33pm ET
Nice to see our educational tax dollars at work on such an important matter.
James Gerace
Phoenix, AZ, USA —  October 10, 2013 12:42am ET
Amateurs and government bureaucrats, what a combination! Our wine group considers 5 ounces an illegal pour. Our 25 ounce glasses will hold a whole bottle of wine, but one pours much less when 8-10 people are sampling the same wine. I pour my own wine in a restaurant because the server over pours in order to sell you another bottle.
Jordan Warnick
Boston, MA, USA —  October 10, 2013 2:04pm ET
Are you kidding me? What a waste of time and money. Next thing will be a study on what is a cup of coffee, 5.25 oz, 6.5, 7.75 or, believe it or not, 8 oz in automatic brewers. Then there's how large is short (8 oz), Tall (12 oz), Grande (18oz), Vente (24 oz) and Trenti (32oz). Will Mayor Bloomberg get involved and limit how much we can pour?

Sit back, pour a glass and enjoy!
Don Pike
Calgary, Alberta Canada —  October 10, 2013 3:25pm ET
In an age where blood alcohol levels are often being lowered from .08 to .05 the size of pour matters for the consumer.As well I have never & will never understand the "need" for a wine glass that could hold virtually a whole bottle of wine.
James Gerace
Phoenix, AZ, USA —  October 10, 2013 10:09pm ET
Is a large bowl a need or a want? It is better for swirling. It enhances capturing the subtle aromas of a fine wine. It adds an elegant ambiance and enhances enjoyment. So there it is, it is both a want and a need.
Richard Birdsall
Jacksonville Florida —  October 21, 2013 4:56pm ET
Could we talk about something as innocent as wine without political preferences intruding? Geez!

Get a glass of overpoured wine and relax!!
Kara Sheffield
Sacramento, CA —  October 22, 2013 3:32am ET
I wish people were better able to gauge the size of wine pours. I work in a wine bar and there would be a lot less complaining about how small the pour looks in our wine glasses.

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