North Rhine-Westphalia’s Cathedral City and capital have long locked horns over who is smarter, better at celebrating Karneval, and, of course, who is better at making beer.
Cologne sticks by its golden pale ale Kölsch, while Düsseldorf proudly knocks back its dark copper-coloured Altbier. Ordering the wrong beer in the wrong place - even outside of the Rhineland - is sure to get you an unpleasant reaction.
In Düsseldorf drinking culture, for example, you might tell someone "Ex, oder Kölner" - meaning "bottoms up, or you must be from Cologne". And Cologne likewise has similar insults for their Rhine River frenemies.
But a new study is sure to burst some bubbles over in the west.
Professor Helmut Quack at the Düsseldorf University of Applied Sciences found in a study published online this week that the two beers taste almost exactly the same.
Quack had 50 men from Düsseldorf and 50 from Cologne do an open taste test where they knew which beer was which. Not so surprisingly, 78 percent of those from Cologne said they preferred their hometown ale - and 78 percent of Düsseldorfers picked their Altbier.
Each side declared “their beer” to taste significantly better than the “foreign” beer.
But when the participants were blindfolded, they couldn’t tell the beers apart. They were asked for each to say whether they liked the beer, whether the beer tasted fresh, whether it tasted mild or whether it tasted herby.
And their answers for each were “nearly equal”, according to the study.
The taste-testers were also asked to try to identify the beer and the results were about the same 50-50 chances as a random coin toss: participants gave the right answer just 55 percent of the time.
“These results are quite amazing, because it is unbelievable that men cannot differentiate objectively between Kölsch and Alt,” the unfortunalely named Quack wrote in the study.
Quack explained that the results could provide great insights for marketing because they show that there is a connection between how something tastes and its colour, brand and emotional meaning to the taster.
But locals found the results less fascinating.
“My dear Professor Helmut Quack,” a columnist wrote for Cologne's Kölner Stadt-Anzeiger newspaper wrote.
“We Cologners do not care that you have found out after 15 years of researching that there’s no difference in taste between Kölsch and Alt… We will stand by Kölsch,” the columnist continued before implying that his study is less than welcome in the region: “Do you actually still have friends?”