A Caffe Nero customer was forced to undergo surgery to remove a piece of wire from her throat when she ate a panini from the coffee chain.
Katherine Willans, 34, had to go to hospital three days after swallowing the bristle, which had come from a brush wrongly used to scrub grills in the Putney High Street branch in south London.
She suffered a drop in heart rate and was put on an ECG monitor while surgeons removed the wire in August 2014.
Willans, a cake shop worker from Ashtead Surrey, who had visited the shop for lunch with her mother says it has put her off paninis "for life."
The coffee chain has now escaped four charges of breaching food hygiene regulations in a prosecution brought by Wandsworth Council - because the shop's workers had brought the wire brush themselves.
The staff ignored strict training procedures because they preferred cleaning with the wire brush, Wimbledon Magistrates Court heard during a three-day trial.
The law demands high standards - especially from large companies serving large numbers of people - and Caffe Nero's system, while good and well thought out, lacked that important aspect of validation and steps that could have helped to ensure procedures were being followed.
A branch manager told the court she "didn't think it was her duty" to prevent staff from using the brush.
Wire brushes were also found in Caffe Nero branches in Clapham Junction, south London, and Boston, Lincolnshire.
Caffe Nero's lawyer Jonathan Goulding blamed "a member of staff but said that the chain were not "criminally liable" for the incident.
District Judge James Henderson agreed and said the chain had "taken all reasonable precautions."
In my view, Caffe Nero have made out the defence that they did indeed take all reasonable precautions and exercised all due diligence.
Wandsworth Council described the verdict as "very disappointing."
At the end of the day an innocent Café Nero customer suffered a very serious injury that required surgery under general anaesthetic to put right.
Willans said she doesn't want "an unpleasant experience like this" happening to anyone else.
"Changing Caffe Nero's procedures or protocols could help prevent that happening, but I feel that this verdict doesn't necessarily mean that they will," she said after the verdict.