President Barack Obama visited Ireland on Monday, where he had a Guinness at a pub in Moneygall (the tiny town where his great-great-great-grandfather was born). He remarked that the last time he’d ordered a Guinness in Ireland, during a stopover at Shannon Airport en route to Afghanistan, it was much tastier than any he’d had in the United States. “What I realized is you guys are keeping all the best stuff here,” he concluded. Was the president blarneying his hosts—or is Guinness really better in Ireland?

It is. After the Institute of Food Technologists asked tasters to sample the so-called “black stuff” in 71 bars, 33 cities, and 14 countries over the course of a year, they gave it an average rating of 74 points out of 100 on the Emerald Isle, about 20 points higher than it got anywhere else. “This difference remained statistically significant after adjusting for researcher, pub ambience, [and] Guinness appearance,” the researchers noted.

Freshness is the key factor. Beer is liquid bread, or so the saying goes—both are made out of grains and rich in carbohydrates—and just like a baguette, the fresher beer is, the more delicious it tastes. (Wherever you are, order the kind from the closest brewery, the experts advise.) All Guinness sold in Ireland, the United Kingdom, and North America is made in Dublin—so the time it takes for a keg to cross the Atlantic puts it at an immediate disadvantage. What’s more, since your average Irish watering hole probably sells more Guinness than its American counterpart, the chances are that much higher that a patron there will get a pour from a fresh keg. Regularly cleaning taps and draft lines also helps keep taste at its peak, as the Irish know; when the machinery isn’t thoroughly rinsed, old beer can accumulate and degrade, so that the alcohol in it becomes vinegary. Bacteria and mold can form, too.

Additionally, several beer experts told the Explainer that a publican outside of Ireland is more likely to use an inferior combination of carbonating gases. A proper pint, which has a carbonation level about half that of a normal beer, is served using a precise blend of carbon dioxide and nitrogen. The former accentuates some of the sharper components of the brew. Nitrogen, used primarily to stabilize the head, adds creaminess while mellowing the taste of the roasted barley that gives Guinness its coffee-like flavor (and dark color).

Temperature is important, too. Guinness needs to be refrigerated, but the beverage won’t properly release its flavor when it’s too cold. (Similarly, though most cheeses go bad if left out too long, they taste best at room temperature.) Guinness has a quality assurance team made up of more than 100 experts that travels throughout the United States to ensure the brew is served correctly. But there are a lot of bars in America.

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Explainer thanks Charlie Bamforth of University of California-Davis, Derek Buono of Beer Magazine, Ray Daniels of the Cicerone Certification Program, Steve Parkes of the American Brewers Guild and Travis Rexroad for Guinness.