Local citizens buy qingtuan at Wangjiasha, a time honored restaurant specialized in various indigenous snacks in Shanghai. [Photo by Gao Erqiang / chinadaily.com.cn]

The qingtuans that Li and his family make are filled with diced bean curd, bamboo shoots, garlic and pickles, giving the snack a savory taste. Most of the qingtuans found in shops, however, are sweet in nature.

While the most common fillings include red bean or black sesame pastes, many businesses have been introducing new flavors every year to set themselves apart from the competition.

For example, in 2016, Shanghai dessert maker Xing Hua Lou debuted a qingtuan which was filled with egg yolk and dried pork floss. This variation is till today still highly popular with customers.

This year, Xing Hua Lou has introduced new savory options such as sliced chicken with bacon and beef with cheese. Other shops like Shen Da Cheng are selling a milk and mocha-flavored qingtuan which resembles the Japanese dessert mochi, while Ningbo Tangtuan has released a version with durian paste.

According to Li, the paste is made by mixing butter with durians imported from Malaysia, a country renowned for its production of the fruit.

Despite its pungent smell, the durian snack has proved to be popular among customers, accounting for one third of the shop's total qingtuan sales.

Although stores usually sell qingtuans that are refrigerated or stored at room temperature, Sun Wenji, who grew up in Suzhou of Jiangsu province, said that freshly steamed ones taste the best.

"The qingtuan is best eaten when it is hot. This is when you can smell the refreshing scent of the reed leaf underneath the snack," said Sun.

Despite its popularity in the Yangtze River Delta, the qingtuan has yet to become a national snack like the zongzi, which is consumed during the Dragon Boat Festival in summer, or the mooncake, which is staple during the Mid-Autumn Festival.

As such, Sun has had to settle for refrigerated options that she buys online as the snack is difficult to find in Beijing where she currently works.

"I really miss the qingtuan from home," she said. "But I guess having a cold qingtuan is better than nothing."