How many calories are in a glass of wine? It's often difficult to tell. Even though the U.S. Treasury department approved the voluntary addition of the information on labels of wine, beer and spirits in 2013, it hasn't become an industry standard to include it. Sometimes you can find the information on a winery's website, but it's not common.

That may be starting to change.

Treasury Wine Estates taking a first step

Treasury Wine Estates (TWE) owns almost 50 wine labels all around the world including several well-recognized U.S. labels such as Beringer, Stag's Leap and Cellar No 8. TWE recently announced that it will provide calorie information for all the wines it sells, according to Drink Business.

The company's general manager for Europe, Dan Townsend, said the calorie counts are being provided for consumers who are "increasingly interested in accessing the facts on calorie content to help them make more informed choices on alcohol consumption. Because of TWE's significant number of labels, Townsend said this step "leads the wine industry in responding to consumer interests in this important area."

The information will be provided online, and each bottle will have a dedicated website address on its label to lead consumers to the information. The calorie counts will not be printed directly on the label.

When (and where) you'll see it

In the United States, it will be a couple of years before we'll see web addresses printed on labels. 2016 vintages of wines sold in Europe will be the first to have addresses because European lawmakers have been pushing for calorie counts on alcohol already. The Americas, Asia, Australia and New Zealand will see labels later down the line.

wine bottle and glass next to a laptopWith calorie labeling on wine, you actually check the label for the website and that's where you go for nutritional information. (Photo: artjazz/Shutterstock)

Why add calorie information to wine?

European Union lawmakers are pushing for mandatory calorie labeling on all alcohol, not just wine. The idea is that people should be aware of just how many calories they are consuming, just like they do when they drink almost any other beverage.

While TWE is getting ahead of this possible mandatory labeling, many European wineries are against it because calories vary from vintage to vintage. Sugar levels in wine change with each vintage so wineries would have to test yearly for the calories in each wine they produce. This could be financially devastating for many small wineries, something a large organization like TWE would not have to worry about.

There's also an interesting variable when it comes to the accuracy of calorie information for wine, and it doesn't have anything to do with vintage. It has to do with age. As a wine ages, the calories of the wine in the bottle may change, according to Aurora Abad, policy officer for the Comité Européen des Entreprises Vins, the wine industry's European body.

Will consumers change their drinking habits based on calories?

Will people drink less if they are aware of the calories in the alcohol they're drinking? That's another concern some European wineries who oppose mandatory calorie counts have. They fear that when drinkers realize that a bottle of red wine has as many calories as half of a pack of digestive biscuits (a type of popular cookie), they will drink less.

Winemakers may have nothing to worry about, at least not here in the United States. A 2013 Carnegie Mellon study showed that putting calorie counts right on the menu in places like McDonald's and Starbucks had no effect on most people's choices. Even when the menus gave additional information, like the recommended daily intake of calories, it still made no difference.

Right now, calorie labeling on wine is not mandatory in Europe or in the United States. TWE is only the second company to do this voluntarily. Diageo announced earlier this year that it would be providing nutritional information, and the way that information would appear for its beverages would vary depending on each country's rules and laws. While these are both large companies, they still represent only a small fraction of the producers of wine, beer and spirits sold in the United States. Chances are other producers will be watching to see how consumers receive this information before voluntary calorie and other nutrition labeling become industry standards.

Robin Shreeves ( @rshreeves ) focuses on food from a family perspective from her home base in New Jersey.