A Shanghai restaurant owner was sentenced to three and half years in prison and her employee was sentenced to one year after they were found guilty of manufacturing and selling toxic or harmful foodstuff by using gutter oil, or recycled cooking oil, in hotpots served in their restaurant.

The pair was sentenced by a court in Shanghai's Huangpu district on Thursday. It is the first time restaurateurs in Shanghai have faced criminal charges for using gutter oil.

Zheng Pin, 38, and her nephew Zheng Wei, 26, admitted to using gutter oil to cut costs since last June.

The pair ferried waste cooking oil they collected in Zheng Pin's hotpot restaurant to Zheng Wei's home, where they filtered it, mixed it with fresh oil, spices and pepper and boiled it for two or three hours. They later delivered it to another hotpot restaurant owned by Zheng Pin's husband to use.

Zheng Pin's husband is not facing any criminal charges.

According to judge Li Qianlan, recycled restaurant waste oil, which is repeatedly used or the by-product of bad fat from animals, is known as "gutter oil".

"Kitchen waste oil contains a large number of toxic and carcinogenic substances, such as aflatoxin," said Fan Zhihong, associate professor of nutrition and food safety at the China Agricultural University. "Gutter oil is difficult to test, which poses great difficulties to the supervision and related departments."

Fan said the country's legal system could be more specific on the definition of gutter oil. "For example, there should be regulations on how many days the restaurant is allowed to use the oil, in other words, be more specific on what's ‘repeatedly used' oil".

Xu Liming, a senior officer with Huangpu District People's Court, said the case "challenged the baseline of social morals and threatened the safety of people's lives". Xu said criminals involved in similar cases relevant to food safety would be "severely punished".

"A 200,000 yuan ($32,140) fine was also given to Zheng Pin," said Xu.

The court also delivered judgments on Thursday on another similar case. Restaurant owner Yu Zhenjiang was sentenced to three and half years in prison for manufacturing and selling toxic or harmful foodstuff and recycling waste oil. The court also fined Yu 200,000 yuan.

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