The owners of two restaurants from Shanghai have pled guilty to using gutter oil, or recycled cooking oil, in hot pots served in their restaurants — the first time owners have faced criminal charges for the practice.

Zheng Pin and her nephew Zheng Wei admitted to having been using gutter oil to cut costs since June.

The people's court of Huangpu district is yet to sentence them.

According to the prosecutors, the pair would ferry waste cooking oil they collected in their restaurants to Zheng Wei's home, where they would filter it and mix it with fresh oil, spices and peppers, and boil it for two and three hours.

The pair were exposed to the local media and they turned themselves in.

"I didn't know it violated the law and I regret it a lot," Zheng Pin told the court.

Prosecutors said the pair's actions were very harmful, and have asked the court to sentence both to up to five years in prison along with a fine.

The defense claimed the pair had no intention of using toxic materials in dishes, and only used "unhygienic and unhealthy" substances, which along with their confessions, should be taken into account during sentencing.

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