Behind the picturesque rows of grapevines at vineyards around the world, winemakers are bending the truth.

It’s not the sort of thing most wine drinkers would have noticed, because it’s happening behind the scenes, before bottles are shipped out, and it’s tough to tell by taste. But it’s hard to imagine anyone would appreciate it.

Many winemakers have been a little loose with the information shared on their labels. Not with the region, vineyard, year and varietal, which people — both expert and not — look to when buying wine, but with the alcohol content, which they have been misreporting on bottles for decades.

The percentages reported on bottles aren’t the precise measurements consumers likely believe them to be. A number of factors, including tastes, expectations, associations, rating systems and even international tax laws appear to be nudging winemakers to round the alcoholic kick of their respective wines up or down a notch on labels in ways that might make the bottles more attractive to prospective drinkers. And the problem is widespread.

“The errors, whether deemed ‘small’ or ‘large,’ are systematic,” said Kate Fuller, who teaches agricultural economics at Montana State University.

This past fall, Fuller, along with a team of researchers that included Julian Alston, a professor in the Department of Agricultural and Resource Economics of the University of California at Davis, and James Lapsley, a retired professor who has written and researched extensively about wine, set out to test two theories. The first was something experts have been warning about for some time: Wines, for various reasons, have been getting more alcoholic. The second was something else: Winemakers have been inaccurately reporting the alcoholic contents of their wines.