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Preventing Foreign Material Contamination. What Works. What Doesn’t.

Posted in Food Policy,Food Safety,Our Blog on February 27, 2019

Foreign material contamination occurs when something not intended to be included or consumed ends up in the food.  This is becoming a growing food recall topic despite the many different ways that food manufacturers can prevent and detect this type of contamination before it leaves the facility.

Depending on the food of interest, there are inherent material risks and those completely avoidable.  Shells, seeds or pits, bone fragments.  These are items that sometimes make their way into food by mistake.  Other contaminants such as glass, metal, or plastic are often a result of improper maintenance or a production problem.

Avoidance and prevention are always the best policy, but what can companies do to detect these potential foreign materials so they don’t end up in the supermarket, home kitchens, and eventually your family’s mouth?  Well…  There are many options.

Metal Detection

Metal detection is optimal for detecting, well, metal in foods.  Food industries often employ one or more of three different detection methods – pulse technology, ferrous in foil detectors, and balanced three coil detectors.

  • Pulsed metal detectors: These types of detectors are great for detecting large metal pieces. Think nails or cans that can be found in bags of raw material.
  • Ferrous in foil detectors: When foods are packaged in foils tray packaging, ferrous in foil detectors are necessary. These detectors can eliminate the foil interference to detect metals present in packaged foods.
  • Balanced three coil detectors: The most common type of metal detection equipment used in food manufacturers and processors. This is due to their high sensitivity.  This method can detect metal shards in a variety of packaging material including paper, poly film, cardboard, and metalized film packaging.

Metal detection methods are not without their limitations.  The type, shape and orientation of the metal contaminant can affect the detection ability.  Operating frequency, position of contaminant, type of product, and potential environmental conditions such as vibration affect sensitivity of detection.


Magnets are common tools for detecting metal contamination in food.  This is due to the simplicity of the process and inexpensive investment.  Installation and retrofitting are easy and requires minimal disruption.  Maintenance of magnets are also fairly low, and they are easy to clean.

Magnetic separators are a common part of food production facilities.  Permanent magnets and electromagnets are common types employed.

Magnets do have their limitations.  They can only detect ferrous contaminants.  Phosphor bronze and brass are off the table.  Some foods offer limitations as well.  Processed foods, cakes, and bread are dense.  Magnets are limited in their ability to pull contaminants out.  Metal products are are trapped in bottled, canned, and packaged foods making magnets useless for retrieval in these products.

Optical Sorting Systems

Optical sorting systems use color detecting technology to separate unwanted objects – objects that do not meet a specific range of color.  The range is more sensitive than that detectable by humans.  This method is great for detecting glass, sticks, stones, insects, rotten matter, etc.

Manufacturers pass food products through an optical box that views objects from several different angles, measuring the reflectivity and color of each object to detects anomalous objects and contaminants.

Limitations are related to the desired sensitivity of the optical sorting machine.  The more sensitive the machine is set to, the potential for good products rejected increases.  However, if sensitivity is decreased, the risk of potential contaminants going undetected increases.  The manufacturer must achieve a delicate balance for sensitivity for best results.

Microwave Reflectance

Microwave reflectance technology is a new and desirable method for foreign material contamination detection.  The problem with this, is that there are limited number of devices.

This technology uses microwave emission and reflectance detection to allow a food manufacturer to detect a wide range of contaminants, including small contaminant particles.  Locating the contaminant after detection is also very easy with this method.  For those lucky enough to have this technology, it is very useful.

Nuclear Magnetic Resonance Imaging

Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) are perfect for detecting bone fragments and other foreign materials in meat products such as beef, pork, fish, and poultry, though application in whole fruits and vegetables looking for foreign bodies, worms, and holes are also beneficial.

NMR can be used to obtain quality measurements in fruits and vegetables as well.  Bruising, internal browning, ripening, fungal infection, and even sugar content can be detected with magnetic resonance technology.

The disadvantage?  Cost.  Magnetic resonance technology is very expensive and outside of the need for many food manufacturers despite the obvious benefits.  Alas, until the technology becomes more affordable, other detection methods will continue to thrive.

Surface Penetrating Radar

Surface penetrating radar also uses electromagnetic radiation to detect foreign bodies in food.  It also uses microwaves, albeit low power microwaves.  Usefulness is not limited to foreign material detection with this method.  It is also great for quality control to be sure that required ingredients are present in the food product – for example, detecting peanuts in a chocolate with peanut bar.

Surface penetrating radar sends out electromagnetic waves and detects the delay in signal that bounces back to the detector.  This method allows for detecting both metallic and non-metallic contaminants, though it does have a weakness.  Metallic packaging.  Metals in the packaging do not allow the waves to bounce back properly, impeding detection of any contaminants enclosed.

Electrical Impedance

Electrical impedance combines conventional metal detection systems with microwave-based systems.  Radio and microwave frequencies are emitted and returning signals are measured by an impedance spectrometer.

This technology works better than a conventional metal detector in its ability to detect a wider variety of contaminants.  Wood, glass, and plastic are on the table with electrical impedance.

Despite the obvious benefit, this technology is not yet mainstream. Additional development is needed to allow the technology to be calibrated to specific food sources.  Calibration ability and ease seem to be its limitation.


X-ray technology is widely used due to the wide variety of contaminants it is able to detect and the ease of operation.  In addition to metals and non-ferrous metals, x-rays can detect stones, glass, PVC plastic, Teflon plastic, concrete, ceramic, and bones.  Other quality uses include the ability to detect sugar or flavor clumps as well as missing components in food products.

The x-ray technology used in food manufacturing is different from what is used in the medical industry.  Radiation emission is significantly lower, and rest assured it will not make your food radioactive.

These machines require minimal training to operate and can allow a high production rate with fewer false rejects, increasing manufacturing profitability.  Higher-end models are even easier to use with electronic interfaces and displays.

X-rays are not without their own limitations.  Contaminants with low densities such as paper, cardboard, wood, hair, thin glass, and low-density plastics are undetectable.


Ultrasound technology is a non-intrusive and non-destructive foreign material contamination detector. It detects a wide range of contaminants with fewer costs and is safer compared to x-rays.  High production can be maintained due to fast scanning process with this technology.

Separation Systems

Separation Systems often use size exclusion technology to detect and remove contaminants and foreign bodies from raw materials and ingredients.  Sieves and filtration methods are the primary method of separation systems.  Other methods include weight detection in the manufacturing and packaging process.

This method is not 100% accurate at removing contaminants, though it is widely used by food manufactures to demonstrate they have attempted to remove contaminants from their products.

What Method is Best?

So…  What method is best?  That depends.  When a food manufacture researches the best method for detecting and removing foreign material contaminants, several factors are evaluated.  First, the type of product they manufacture and technologies that might work for it.  Second, the limitations of the available products considered.  And finally, the cost/benefit analysis for the final options.

Regardless of method chosen, consumers hope that food manufactures make the best decision to avoid potential harm and business owners how they make the best decision to maintain profitability and reduce risk of costly recalls.

By: Heather Van Tassell, Contributing Writer (Non-Lawyer)