"There was a maintenance program undertaken at the time and it appears there was an isolated issue with the metal detector on one particular day," he said.
"We have taken the step to undertake a voluntarily recall of the whole batch.
"We are aware of two packets in this particular batch of 5808 which contained metal fragments. As a precaution, we have issued a voluntary recall of this batch, which was distributed to the major supermarkets in November last year."
So far, there have been no reports of illness, but anyone concerned about their health should seek medical advice.
The spokesman said this was the first time in 37 years that the business has had to undertake a recall of one of their products.
For more information go to the FFOWCS Williams Ltd website or call 09 849 2394.