A Caffe Nero customer swallowed an inch long metal bristle when eating a panini and was forced to have emergency surgery.
Katherine Willans, 34, was eating a panini in the Putney High Street branch of the coffee chain when the bristle became lodged in her throat.
Ms Willans was ill for three days before being rushed to hospital on 3 August, 2014.
Doctors found the bristle - from a wire brush wrongly used to clean a grill - in Ms Willans throat as she underwent emergency surgery.
Caffe Nero was cleared of four counts of breaching food hygiene regulations by a judge at Wimbledon Magistrates Court.
The court was told staff ignored strict training procedures and brought in the wire brush because they thought it was more efficient.
A number of staff testified during the three-day trial to say they regularly used the brush, despite knowing it went against procedure.
The Mirror reports District Judge James Henderson saying: "It is easy to think of other steps that might have been taken, but it seems clear that this was indeed indoctrinated into employees during various stages of their training.
"In my view, Caffe Nero have made out the defence that they did indeed take all reasonable precautions and exercised all due diligence."
In a statement to The Independent, a spokeswoman for the coffee chain said: “Whilst prosecuted as a result of the injury caused to Ms Willans at their Putney store, Caffe Nero is pleased that the Court dismissed all charges against it and sees it as a vindication of its systems.
"Whilst Caffe Nero regrets the injury caused to Ms Willans the Court accepted that her injury was caused by an unknown member of staff’s actions which were unauthorised and prohibited by the Company."
She also pounted out that the company has never been convicted or cautioned in relation to any food safety matter.
