New York delis like Katz’s Delicatessen, above, surged in popularity during the interwar period in the 20th century. (Andrew Burton / Getty)

To the chagrin of many area sandwich enthusiasts, D.C. has never been a city known for delicatessens. “I would call that generally accepted knowledge,” Ted Merwin says. “Why that’s so, I really don’t know.”

And if anyone would know, it’s Merwin: He’s the author of the 2015 book “Pastrami on Rye: An Overstuffed History of the Jewish Deli.” In it, he insists that to find true pastrami nirvana, you have to head to the Big Apple. Though delis have been around New York since the turn of the 20th century, their popularity hit a peak during the interwar period, when a second generation of Jewish immigrants flooded the entertainment industry and created a market for sandwiches in Manhattan’s theater district.

Merwin — the executive director of Baltimore’s Beth Am Synagogue and a former Judaic studies professor at Dickinson College who holds a doctorate in theater — will moderate this weekend’s Smithsonian Associates program “Where Harry Met Sally: The Cuisine and Culture of the New York Jewish Deli.” The talk will cover the Jewish deli’s origins and its place in pop culture — with lunch (of course) provided by D.C.’s DGS Delicatessen.

And if you think you already know everything about Jewish delis, Merwin can set you straight on a few things.

Not all Jewish delis are kosher.
Not all food at Jewish delis follows kosher rules — and some kosher delis even cheat. For example, Merwin says: “You’re not supposed to have business open on the Sabbath. But there are definitely kosher delis that are open on Jewish Sabbath and Jewish holidays.”

Delis weren’t always all about the sandwiches.
“[Delis] started as takeout stores, so they were ‘delicatessen stores’ in the newspapers in the turn of the 20th century,” Merwin says. And at these “delicatessen stores,” gourmet meats were sold. “Sandwiches became popular later, particularly in the 1920s.”

A famous brand of cream soda was born from celery tonic
Dr. Brown, the name on the cans of cream soda still sold today, got his start in the 1860s dispensing his celery tonic to children in New York’s Lower East Side suffering from stomach problems, “which makes sense if they’re eating a lot of this kind of food,” Merwin says. Brown started bottling cream soda, which remains a deli staple today. “The sandwiches were so greasy that you’d need something carbonated,” Merwin says.

S. Dillon Ripley Center, 1100 Jefferson Drive SW; Sun., noon, $130, sold out. Wait list open at 202-633-3030.