"It's easy to obtain poppy capsules from familiar sources," said Fan Shengwu, deputy secretary-general of the Henan Provincial Restaurants Association. "Campaigns are only temporary remedies, and lawbreaking will resume."

The city of Leshan, Sichuan province, launched a campaign in 2008 to crack down on the use of poppy capsules after city authorities found 12 out of 401 restaurants used the substance in hotpots.

The SFDA in March 2009 carried out special inspections to root out this practice.

Fan suggested that law enforcement agencies involve industry associations in long-term management, because they know the actual situation better than inspectors, who can be fooled if restaurants hide supplies of illegal additives.

"An association can unite its member restaurants to make a commitment and wipe out stubborn bad practices together" and expose restaurants breaking the law, he said.

Technology and cash - higher rewards for whistleblowers - are good ways to punish lawbreakers, according to some food safety experts.

"Electronic monitors in restaurant kitchens can provide a panoramic view of the action," said Qiu Baochang, head of the lawyers' group of the China Consumers' Association.

Local governments and officials should also take responsibility for food safety, Qiu said.

"The governor should be dismissed from office upon the occurrence of any food scandal and not get another post for the rest of their life. It's like those who have a record of drunk driving being barred from driving forever," he added.