HO CHI MINH CITY - A Vietnamese family-run coffee manufacturer based in Dak Nong province has been caught producing "dirty" coffee from harmful materials like used batteries, dirt and rock dust, daily newspaper Tuoi Tre News reported on Wednesday (April 18).

The facility, owned by Nguyen Thi Loan, was raided by local police and food inspectors on Monday afternoon following tip-offs from residents who were suspicious about the activities being conducted on the premises.

According to authorities, 12 tons of the "dirty'"coffee were seized during the raid.

Some other raw materials used in production were also found. They included 35kg of black powder extracted from used batteries and a bucket of black liquid weighing around 10kg.

The owner told police she would buy rejected coffee beans from other facilities at low prices. The beans would then be ground and mixed with other "ingredients" such as dirt and rock dust. Finally, the mixture would be dyed black.

Loan admitted that her factory has been in operation for years and that she has sold over three tons of her "coffee" on the market this year.

Police have taken samples of the coffee for lab tests, Tuoi Tre News said.

Associate Professor Tran Hong Con, a chemistry expert from the Vietnam National University, said the black substance found in D batteries is a toxic chemical called manganese dioxide.

Manganese dioxide is a highly oxidant compound, and as little as 0.5 milligrams of it mixed in a litre of water is enough to cause manganese poisoning in humans, Prof Con told Tuoi Tre News.

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Manganese poisoning, also known as manganism, can cause brain damage after prolonged exposure. It was a condition common among manganese ore miners in the 19th century. The poisoning is irreversible and can lead to hallucinations and death.

Other heavy metals commonly found in batteries such as lead, mercury, zinc, cadmium and arsenic are also extremely toxic; they can damage one's brain, kidney, cardiovascular system and fertility if consumed, Tuoi Tre News said.

Brazil, Colombia and Ethiopia are among the world's largest coffee producer. Vietnam is fast catching up with a reported 2.6 million people in the country employed by coffee manufacturers.

During the 1990s, coffee production across the country grew around 20 to 30 per cent each year, according to Newsweek.