On the restaurant-rating app Dianping, most of the dregs vinegar hotpot restaurants in Beijing are newly opened, and some of them are still undergoing decoration. Also, some restaurants that used to feature another Hainan delicacy, coconut chicken hotpot, are now launching a two-flavor hotpot that serves both the coconut chicken and the dregs vinegar soups.

Within the category, Lanhaiyi dregs vinegar hotpot is one of the most popular choices in Beijing. With two branches already opened this year, two more are under construction.

Lang Lang, co-founder of the restaurant, recalls that she and her friend decided to open the eatery last August, and they spent a month in Hainan researching and learning more about this local delicacy.

"The taste of the dregs vinegar soup base is new for Beijing diners. Compared to other types of hotpot, it doesn't use much oil, which caters to the healthy eating trend of recent years," Lang says.

From Wenchang and Sanya to Haikou of Hainan province, the duo tasted all iterations of dregs vinegar-based food they could find before they started to develop their own recipe.

"There is no standard for the soup. Each store has its own recipe — some add fried garlic, while others add raw garlic," Lang says. "For Beijing diners, we want our version to have a rich and balanced flavor."

After dozens of rounds of trials, Lang has finally settled on one version that she is satisfied with, which adds shredded seafood. They found a local factory in Hainan to make the soup which takes around a month to produce and is shipped by air to Beijing.