Along with carving the ham and eating gingerbread cookies to our hearts’ content, there’s another big food tradition that comes on Christmas day.

For over a century, Jewish families in the U.S. have been paying a visit to their favorite Chinese restaurant for a special annual meal.

Today, the occasion has become such a tradition that Chinese restaurants fill up quickly and see business boom for the day. New York City’s Shun Lee, for example, has received around 1,300 reservations for the day in the past.

But while people now excitedly anticipate the popular custom, its roots are bittersweet. Though there are several theories as to how this practice began, some experts agree that it’s rooted in finding unity amid adversity.

Being the two largest immigrant groups at the turn of the century that weren’t Christian, Chinese and Jewish people both understood “what it’s like to be outsiders.”

Jennifer 8. Lee, producer of “The Search for General Tso,” explained to The Atlantic that being the two largest immigrant groups at the turn of the century that weren’t Christian, Chinese and Jewish people both understood “what it’s like to be outsiders.”

It was at Chinese restaurants that Jewish immigrants felt accepted, she said.

“Jewish people could go into Chinese restaurants and feel safe,” Lee explained to First We Feast. “And during the 1920s, Chinese food was exotic and cosmopolitan, so the way to impress a girl was to go grab some chop suey.”

Michael Twitty, Food writer and culinary historian, told the outlet that the custom was also a way for the two groups to create their own uniquely American experience.

“How do you affirm your Americanness when the ‘American’ thing to do is celebrate Christmas?”

“How do you affirm your Americanness when the ‘American’ thing to do is celebrate Christmas?” he said. “You create your own ‘Christmas.’”

Another factor that’s been cited as the root of the tradition is how close in proximity the immigrant groups settled.

Ken Albala, history professor and chair of Food Studies at University of the Pacific’s San Francisco campus, explained that most Jews came to the U.S. in the late 1800’s by way of Manhattan’s Lower East Side ― an area just under Chinatown.

Living and working in close proximity allowed for interaction between the two cultures “to which food and cultural cuisine holds great importance,” he told Mic, later adding that as Jews spread into different neighborhoods, Chinese food did too.

Chinese and Jews find some common ground when it comes to the actual food as well.

“Chinese food allowed Jews to eat foreign cuisines in a safe way.”

Jewish law prohibits the mixing of milk and meat in cooking and Chinese cuisine doesn’t feature dairy at all. However, other popular ethnic cuisines like Italian and Mexican food do combine the ingredients quite a bit, limiting the types of dishes Jewish people can experience, Lee explained to the Atlantic.

“Chinese food allowed Jews to eat foreign cuisines in a safe way,” she said.

As for the pork and shellfish in Chinese food ― well, some immigrants were willing to bend the rules of tradition just a bit, Albala said.

“As kosher regulations loosened for many immigrants, they were happy to try pork, shrimp and other un-kosher dishes in proximity.”

While the way Christmas is observed has evolved over time, the Chinese meal has stayed as an essential tradition; one that’s part of the Jewish experience in the United States.

“I’ve had traditional Christmas dinners in the midst of warm Christian families, and I’ve had numerous Chinese meals on Christmas day,” Rob Eshman, Editor-in-Chief of Jewish Journal told First We Feast. “But for me, Chinese is the real taste of Christmas.”