Green rice balls are available all year round, but demand spikes a few weeks ahead of the annual Qingming Festival.[Photo By Gao Erqiang/China Daily]

"I apologize if there isn't anyone who can help answer your questions. The chefs here are paid according to the number of rice balls they make," says Liu Chongliang, general manager of the 71-year-old restaurant and snack shop, Wang JiaSha.

The traditional snack is an important element in the annual Qingming Festival (Tomb-sweeping Festival) when people visit the graves of their ancestors and family members.

The tradition of eating green rice balls on this occasion dates back thousands of years in southern China when people deemed it as a form of tribute to their ancestors.

The grave would be tidied before the rice balls were presented together with some dishes as well as wine and fruit.