Ninety-five percent of Shanxi mature vinegar is made with chemicals, China National Radio reported on Saturday.

China consumes a total 3.3 million tons of vinegar every year, but authentic mature vinegar from Shanxi Province accounts for less than 5 percent, said Wang Jianzhong, vice-president of the Shanxi Vinegar Industry Association.

Mature Shanxi vinegar is one of the four most famous kinds of Chinese vinegar alongside Zhejiang, Sichuan and Fujian provinces.

With origins dating back to 770BC, Shanxi vinegar has a history of more than 3,000 years, according to official Ministry of Culture website www.chinaculture.org.

Blending vinegar with chemicals doesn't violate any Chinese law, but according to the 2000 national standards for vinegar, synthetic vinegar must contain at least 50 percent fermented vinegar.

Rice, sorghum and other ingredients for vinegar are supposed to ferment at high temperature for a month or longer. Blending with acetin can shorten the process to a day or less, the Beijing-based channel reported.

"As long as the acetin content is within the required ratio, it does little harm," Fan Zhihong, a professor of food safety at China Agricultural University in Beijing, told the Global Times.

"Customers don't need to panic. After all, you won't drink as much vinegar as water," Fan said.

To buy authentic mature vinegar, customers should pick brands labeled "fermented" and avoid the cheap stuff, Fan said. Shake the bottle, check its color and texture: Fermented vinegar is brown-red and a little dense.

The Shanxi Food Quality Supervision and Inspection Center issued a statement on Saturday, warning customers that not all products labeled Shanxi mature vinegar were produced in Shanxi Province. Mature vinegar produced in Shanxi is safe, the center announced.

Shanxi's 125 vinegar companies produce 600,000 tons a year. Famous brands include Shuita, Donghu, Zilin, Laifu and Yiyuanqing.

A new national standard for Shanxi mature vinegar will be promulgated in the next six months. The two-year shelf life will be abolished as Shanxi mature vinegar with no preservatives is suitable for longer-term storage and use, according to the Legal Evening News.