In an incident in 2008, a New South Wales pub was forced to apologise to an Australian family and reportedly paid a settlement of $50,000 after a woman was served a chocolate ice-cream laced with human faeces. The incident high-lighted the importance of food forensics, with testing to prove that the contaminant was faeces in the first place, and two DNA tests to try and work out who the faecal matter came from.

In two other New Zealand cases in November 2008, a Christchurch man found a fly baked on his takeaway pizza and Nelson man found his factory wrapped chicken covered in fly eggs. Unfortunately food contamination is not uncommon. Strange smells, weird tastes, cockroaches, metal, hair, fingernails, teeth, cigarette butts, flies, rodent faeces, bones, mice, syringe needles and glass are all things that New Zealand’s food detectives have seen in our food.

Scientists as food detectives

When someone finds something in their food that shouldn’t be there, the New Zealand Food Safety Authority, or sometimes a private or commercial client, has a team of scientists from ESR (Environmental Science and Research) try to work out how it got there. There might be many reasons for finding out this information. There might be something wrong with how the food is processed, such as broken machinery or poor food handling practices. Alternatively someone might falsely claim they have found a contaminant and the food manufacturer is trying to protect their reputation, or the case might be genuine, as in the Australian example above. Scientists can help provide evidence as to where the contaminant came from.

There are many different types of scientists who become food detectives, they work as a team. One team member might be an expert on insects (an entomologist), another team member might know every different type of metal. Some scientists might be chemists and some might be plastic experts. Even geologists might be called in to identify grit or pieces of asbestos.

Darren Saunders, a Food Chemistry Technical Advisor at ESR, says that food forensics is like the popular TV crime drama CSI, only without the dead bodies – at least not dead human bodies.

The scientists use many different techniques in food forensics. A contaminant might first be examined under a microscope. From this they can often tell what an object is or what the object is made from, and often whether an object has been cooked.

Rodent contamination

Quite a few cases are about suspected rodent (rats and mice) droppings, especially in cereal. Rodents lick themselves often and swallow a fair bit of their own hair; as a result there is undigested hair in their faeces. Rats also have a special type of hair which helps the scientists identify them when the suspect faeces is smeared onto a microscope slide. Sometimes they really are droppings, but generally the suspect material turns out to be just grease, burnt raisins or currants.

There have been legendary cases where people have found dead mice, or pieces of mouse in their food. Mr Saunders says that because mice are everywhere it is not possible to use their species to pinpoint geographical origin (as you often can with species of insect contaminants). “However, it’s possible that the pollen caught in its fur can tell us where it came from.” Determining where something came from is important, particularly when New Zealand might be in dispute with another country about contaminants in their food we have imported.

Glass contaminants

Glass in food is another common contaminant. For a piece of glass with a curved surface the scientists do some maths to work out the size of the original object. For example, windowpane glass is flat on both sides and about 3 millimetres in thickness, this is very different to glass from a light bulb, which is curved and a lot thinner. As well, there are several sorts of glass that are only used in particular products so the scientists use energy dispersive X-ray analysis to tell them the type of glass involved. “This can tell us whether the contamination is from domestic glassware, window glass or lead crystal, Pyrex or tableware,” says Mr Saunders.

Some times things that look like glass aren’t glass at all; they prove to be sugar, salt or other types of crystals. “What looks like glass in wine can prove to be tartaric acid crystals and merely an aesthetic issue.”

Metal contaminants

Food factories are full of metal, so it’s not surprising that pieces of metal are one of the most common bits of rubbish you can find in your food. Things such as mixers, rollers and pumps regularly end up with pieces coming off. After being examined under the microscope, a metal object can be examined by a special scanning electron microscope that tells the scientists exactly what is in the metal.

There was a case where a man thought he had found a piece of metal in a loaf of bread. When the scientists looked at the object under the electron microscope it showed that the piece of metal had an unusual mixture of mercurysilver and copper. The types of metal usually found in a food factory are things like cast iron or stainless steel, certainly not these rare metals. After a bit of head scratching the scientists worked out that there is only one use for that mixture of metals and that was in dental fillings. It turned out that the man who complained about the metal had lost a filling at the time he was eating the bread and hadn’t realised the metal was his rather than the bread maker’s.

Discovering false complaints

The scientists are also often able to tell at what stage a piece of rubbish enters the life cycle of the food. For example, when bread is baked, the dough will form a neat shape around the outside of the contaminant. If it has been put in after baking, the bread doesn’t have the shape formed neatly around the item.

Not all complaints are as innocent as the man with the lost filling. A student complained that he had found a fly in a meat pie. However, after an insect expert had cut the fly open under a microscope, he could tell from its insides that it had not been cooked. In fact the fly had been dead for sometime and had probably died of natural causes.

In another case involving a cockroach in a restaurant meal, scientists were able to copy a thumb-print off the back of the cockroach - the thumb print belonged to the man who complained.

Useful link

ESR (the Institute of Environmental Science and Research) is New Zealand’s Crown Research Institute that specialises in science relating to people and communities.


    Published 4 December 2008