BEIJING -- Chinese experts on Thursday called for stricter measures to supervise the production of cooking oil, yet admitted that finding a method to identify used cooking oil or "gutter oil," was likely too difficult.

Deng Haihua, spokesman for the Ministry of Health, said comprehensive measures should be taken to conduct enhanced inspections and eliminate gutter oil processing bases in order to protect food safety.

Wang Zhutian, a food safety expert, said relevant departments will make joint efforts to develop tests to detect gutter oil, but admitted that it is very difficult to identify it and the cost is too high.

Last month, police arrested 32 suspects from a criminal network spanning 14 provinces that allegedly produced "gutter oil" and sold it to restaurants. More than 100 tonnes of the oil was seized.

After that, authorities set up a panel of 13 experts who specialize in cooking oil processing, food safety and chemical analysis, to find a method of identifying the illegally recycled cooking oil.