The recipe for Kalles was sold by a peddler to Abba Seafood, a defunct Swedish company, in the early 1950s, for 1,000 Swedish kronor, or less than $200 at the time. It was originally sold in plain tubes, according to an account on Orkla’s website. But the tubes were soon made over to feature Swedish colors — blue and yellow — and a picture of the son of the chief executive of Abba Seafood. The son, now grown up, receives a free lifetime supply.

The formula seemed to hit a sweet spot in a caviar-loving nation, and a million tubes sold in the first year. Orkla acquired Abba in 1995. Today, the company sells about 3,300 tons of Kalles a year.

Some people eat it on bread, some with cheese, but about 60 percent eat it with eggs, typically with slices of boiled egg, according to Orkla’s research.

“I suppose the U.S. equivalent would be peanut butter,” said Jonas Aurell, who along with his wife, Bronte, owns ScandiKitchen, a London cafe and marketplace that sells Scandinavian food, including Kalles.

“Scandinavian food traditionally has a lot of pickling, curing, salting,” he added. “This is salted cream cod roe, it just ticks all the boxes for us.”

He said he grew up eating it, and now it was second nature.

“I eat it — I wouldn’t say every morning — but if I have eggs, I have to have that.”

Image ScandiKitchen sells Kalles, which is often served with a boiled egg. Mr. Aurell compared Sweden’s taste for it to the American love of peanut butter. Credit... Tom Jamieson for The New York Times

Kalles’s omnipresence does not travel across the border to Norway, where Norwegians prefer other brands of caviar in a tube, particularly Mills Kaviar, which Mr. Aurell said had a stronger taste.