MIDDLETON, Wis.—Three teenage girls were standing in the gift shop of this town's largest museum when they were asked a question by the curator.

"Want to do the Poupon U cheer?" he said. Soon the four began to chant: "Who needs Harvard, who needs Yale? At POUPON U you'll never fail."

The yellow condiment is king here at the National Mustard Museum. The museum boasts 5,568 mustard bottles, 302 antique mustard pots, video clips in the MustardPiece Theater and T-shirts with slogans like, "Friends don't let friends eat k&@#&p."

"A day without mustard is like a night without a quilt," says Barry Levenson, 64 years old, founder, ring leader and "Chief Mustard Officer" of the 21-year-old museum.

Visitors will find a wall packed with 475 old-timey mustard tins next to floor-to-ceiling cases of yellowish squeeze bottles from Israel, Russia and Vietnam. They can check out an original French's Mustard Man mascot and snippets of an old TV show "Hot Dog," featuring Woody Allen and Jonathan Winters. And they won't want to miss an elaborate mustard pot commemorating King George VI and his wife Queen Elizabeth's visit to Canada in 1939.