But now, Ms. Bickel said, young people in Munich, Bavaria’s capital, just grab a thickly buttered pretzel with coffee on the way to work.

“It’s like Starbucks,” she said. “There are pretzel chains in every neighborhood.” But older people stick to the tradition. “You see grandmas in the beer garden, having weisswurst and a pretzel at 11 a.m. with their first beer of the day,” she said.

Image Ms. Kulchinsky at Sigmund Pretzel Shop. Credit... Evan Sung for The New York Times

In Baden-Württemberg, in southwest Germany near France and Switzerland, the pretzels are known for their fat “bellies” and skinny, intertwined arms. That’s the style at Prime Meats in Brooklyn; Frank Castronovo, an owner, learned to make pretzels there.

“The goal is to have two distinct eating experiences, one crunchy and one fluffy, in a single pretzel,” said Jeffrey Hamelman, director of the King Arthur Flour Baking Education Center in Norwich, Vt.

Mr. Hamelman’s first professional baking experience, in 1976, was an immersion course in pretzels. “I worked at a stellar German bakery in Northampton, Mass., when most Americans were still eating Wonder bread out of plastic bags,” he said. “The owner was German, but her bakers were French, and none of them wanted anything to do with pretzels. So she hired me just for that, and taught me all the secrets.”

The defining “secret” of pretzels is lye, a powerful alkali that gives them their defining contrast between a creamy white interior and a crunchy, dark-brown, lightly bitter crust. Just before baking, pretzels are dipped into a bath of water and lye, which transforms the starch on the surface so that it can brown quickly, while the interior remains moist. Cold lye solution can burn the eyes or skin, but the chemicals are neutralized by the heat of the oven.