Consumers are thinking twice about dried beans after an investigation revealed a toxic chemical has been illegally used to enhance the appeal of the food.

Dried black beans were often eaten by people in northern China when they could not get fresh vegetables in winter. But some dried bean producers in the city of Chaoyang in Liaoning province have used copper sulfate, a toxic chemical compound, to make them look fresher, according to a report on state broadcaster CCTV.

"I bought dried beans before, but not very much. With the news now, I don't think I am going to buy anymore Fresh vegetables are always safer than dried or salted foods," said Zhou Yi, a resident from Shenyang.

Wang Liqun, a 26-year-old teacher in a Chaoyang primary school, also said she and her family will not buy and eat dried beans any more.

"These awful things are related to pickier consumers, who look for tomatoes that look redder and veggies that look greener, and producers just make use of this to grab consumers," she said.

But she said she was not shocked by the dried bean incident, because "there are just too many such unscrupulous things going on out there."

A sample test conducted by the city's bureau of quality and technical supervision earlier this month showed that each kilogram of the tainted dried beans could contain 16 to 110 mg of copper.

A bureau official said copper sulfate is commercially available but is banned from being used in food processing.

People could suffer stomach aches or even spit blood after ingesting an excessive amount of the chemical.

The bureau told provincial broadcaster Liaoning TV that the dried beans with copper sulfate were produced by five small factories in Dongsanjia village of Chaoyang city.

Dong Yuhua, one of the factory owners, admitted to Liaoning TV that her workers added "stuff" to dye the beans so they could satisfy customers with different preferences for the color of dried beans.

Though the bureau ordered the factories to stop processing beans with copper sulfate in early August, the factories have continued their production.

Their dried beans have even been sold in other cities, including Chenyang, Dalian and Beijing, CCTV reported.

A spokesperson for the Chaoyang Bureau of Quality and Technical Supervision could not be reached for comment yesterday.

But Cai Guobao, a purchasing manager with Dadong, a major food chainstore in Shenyang, said that since now is the season for fresh beans, many people are unlikely to buy the tainted dried beans.