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]

Typical fare

Founded in 1945 by Yao Zichu, a former advertising executive, Wang JiaSha started as an eatery offering typical Shanghai snacks like xiao long bao (dumplings), shrimp-filled wontons and steamed sticky rice topped with "eight treasures" that comprises different types of dried plums and nuts.

It was not until the 1990s that Wang JiaSha added the green rice ball to its menu that had already spanned 300 types of snacks and pastries. Named after a small neighborhood in the same area it was in, Wang JiaSha today has seven outlets in Shanghai and five in Hong Kong.

According to Liu, an average of 50,000 rice balls, priced at 4 yuan ($0.6) a piece, are sold every day at Wang JiaSha before the peak period that falls in the week of Qingming. Sales numbers often triple during the peak.

Liu expects to sell up to 2.4 million balls this year, a 10 percent increase from last year.

"When you can have tomatoes and celery all year round, it is only natural that people flock toward something that is seasonal," says Liu.