After headline-grabbing scares in Australia, there's been a strange and concerning string of New Zealand incidents involving foreign objects in food.

They've included a needle found in a capsicum bought at a Tauranga supermarket; a pin in a strawberry from another supermarket in the city; and more needles found in strawberries from supermarkets in Geraldine and Auckland.

Every find prompts stores to quickly clear their shelves, yet not all have been genuine.

Police recently charged a 28-year-old woman with making a false complaint, and only after Pak'nSave Timaru was forced to destroy a "significant" number of perfectly good strawberries.

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How could we tell whether these objects had been put in food accidentally, or were someone's malicious stunt?

Leave that job to ESR's food forensic scientists.

While their work was variable, they received such complaints regularly – and one of the first things to do was checking the container for DNA or fingerprints.

"Then there is the identification of the foreign objects themselves," scientist Darren Saunders said.

"If you have a thumb tack, needle or a pin you look at simple measurements, like dimensions, then compare it to what's commercially available, analyse its composition – what sort of metal is it – where are these available and so forth."

Foreign objects in food were one of the big concerns ESR fielded from manufacturers and suppliers, which wanted to know where the responsibility lay.

"They will want to know if it is a malicious case of someone inserting, for instance, something sharp and horrible into their bread," Saunders said.

"They'll want to know whether it was baked in.

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Foreign objects in food were one of the big concerns ESR fielded from manufacturers and suppliers, which wanted to know where the responsibility lay. Photo / Alan Gibson
Foreign objects in food were one of the big concerns ESR fielded from manufacturers and suppliers, which wanted to know where the responsibility lay. Photo / Alan Gibson

"We had a series of cases with needles found in baked bread and you could tell from the bag by the tiny holes in it that something had been inserted and which direction it came from – that is from the outside."

Another complaint ESR frequently received involved suspect rodent droppings, which, on the face of it, could be hard to tell from bits of burnt grease or other food ingredients.

"But under the microscope, you'll find faecal material which contains the rodent's hair," he said.

"That's because they're always grooming and consuming their own hair, and hair can often be identified down to a species level.

"Mice hairs for instance are very characteristic."

One complaint involving hair came from a milk company, which was continually finding ginger hairs in its on-line filter.

"We identified it as coming from a cat, so you get this image of the cat waiting until night time and jumping into the vat," he said.

"Literally, the cat that got the cream."