AN Adelaide fish and chip shop has been fined after mistakenly sprinkling food with caustic soda.

Police were called to the southern suburbs takeaway outlet on Wednesday night after three customers reported a strange substance had tainted their food.

It was found an employee had accidentally filled a salt shaker with caustic soda.

One male suffered burns to his mouth and was treated at Flinders Medical Centre. Two other people realised their food was contaminated before they sustained any injury.

Police determined that no criminal offence had been committed and handed the matter to Marion council.

A police spokeswoman said police were satisfied there was no longer a public health threat because all customers had been accounted for and had received treatment.

A council spokesman confirmed yesterday the takeaway shop had been prosecuted over the incident.

"Council's environmental health officers have inspected the premises, recommended that staff undertake a food handling course and issued a $500 fine for selling unsuitable food, which is the maximum penalty for an expiation notice under the Food Act," he said.

"Our inspectors are satisfied that the incident was the result of an unfortunate accident."