Most of the so-called "Shanxi mature vinegar" on the market is actually blended from glacial acetic acid and food additives, China National Radio has reported.

A Shanxi Province speciality for more than 300 years, the vinegar should be made from rice, which is natural and chemical free. But Wang Jianzhong, deputy director of the Shanxi Vinegar Industry Association, said only 5 percent of vinegar on the market was authentic.

"It's a harsh reality for consumers that basically all the vinegar we have is blended," Wang told CNR.

However, the association yesterday issued a statement contradicting what Wang had said. It said all the vinegar produced in the northern province was made from rice rather than blended glacial acetic acid.

The Shanxi Provincial Bureau of Quality and Technical Supervision also said yesterday that vinegar produced in Shanxi was safe to consume.

Wang told CNR that if the label on a bottle said it contained sodium benzoate, a preservative, consumers could tell that the vinegar was not the authentic "mature" product.

"In fact, real mature vinegar doesn't need preservative," he said. "Old vinegar doesn't go bad, which is a typical characteristic of the time-honored Shanxi vinegar."

Wang told CNR that a bottle of real Shanxi mature vinegar took three months to a year to produce, but a bottle of a blended one could be made in a day.

"If your vinegar is blended, you shouldn't cheat consumers that it is 'mature'," he said.

According to the country's quality standard for vinegar, blended varieties are allowed on the market. But current tests can't tell whether industrial acid has been used to make the vinegar.

Wang Zhanyong, an engineer with the Beijing Jinzhongtai Food Technology Development Center, told CNR that some illegal seasoning plants used industrial acid to lower the cost. "Our quality test can't spot the difference from a finished bottle of vinegar," he said.

Doctors said consuming too much glacial acetic acid could do harm to people's mouths, stomachs and intestinal tracts. If industrial acid is used, there could be some heavy metal elements present.