Thirty years after the fall of the Berlin Wall, an invisible border running through Germany continues to resist all efforts to make the country truly whole again. However, this dividing line is not about attitudes to democracy, refugees or Russia, but something more elementary: how to tell the time.

In the northern half of the old West Germany, from Flensburg in the north down to Heidelberg in the south, people use the expression viertel nach zehn (“quarter past ten”) if their clock reads 10.15. Yet in a tract of land that covers the old socialist GDR as well as parts of Bavaria and Baden-Württemberg, the same time would be described as viertel elf or “quarter eleven”.

With so much potential for failed meet-ups and missed appointments, one would have expected one variant to trump the other over time. But a group of linguists who spent two years analysing a large data set have been surprised to find the opposite is true: not only are some vernacular expressions proving surprisingly sticky, but if anything their use is realigning along the old iron curtain.

For an article in the science journal PLOS ONE, published on Wednesday, Adrian Leeman, Curdin Derungs and Stephan Elspass compared metadata provided by more than 770,000 people in Germany, Austria and Switzerland who had taken part in an online language quiz, with language surveys dating back to the 1970s.

On the one hand they found that German, Europe’s most widely spoken mother tongue and often described as its most diverse, is becoming more standardised, especially north of the River Main. Local expressions for non-professional football playing, such as pöhlen in Westphalia or bäbbeln in Saxony are slowly being replaced by the generic term bolzen, in what linguists call “regional levelling”.

Yet the old east-west border is proving an unexpected bulwark against linguistic change, especially when it comes to food. West of the former Berlin Wall, Germans call a pancake a Pfannkuchen; on the eastern side, they emphatically tuck into Eierkuchen or “egg cakes”.

As if to deliberately spread confusion, east Germans use the word Pfannkuchen to describe a doughnut, which is called a Krapfen in the south-west, and a Berliner in the north-west.

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The local Saxon variant for pancake, Plinse, meanwhile, has been pushed back to its Sorbian origins as east Germans rally around the egg cake as a “marker of east German regional identity”, as the researchers put it.

Another staple of German cuisine shows the same trend: a beef patty or meatball is clearly a Frikadelle (from the Latin frigere, “to roast”) in the old west, while east Germans enjoy a dash of mustard with their Bulette (from the French boule) or their Klops, the two vernacular expressions that are crowding old local variants such as Beefsteak or Klösschen.

“In an increasingly interconnected world, in which people are more likely to move house, to commute or to communicate with people from other regions, one might have expected that people are also more likely to speak the same way,” said Leeman, a professor at the University of Bern. “Instead, we found that regionalisms still matter: vernacular language is evidently also a marker of identity that people wear with pride.”