Importance of controlling foreign matter in food production

By Nuno F. Soares on 13 May 2019

Globalization of the food industry has allowed for a more expansive food network that allows for food products from distant areas to reach different parts of the world. Food production, consumption, transportation, and the entire food chain have changed drastically over the past few decades and population growth and advances in technology will continue to drive additional changes. By expanding the food industries reach of products and services we also potentially increase the opportunity for foreign material contamination as well.

Foreign material of any kind can potentially introduce a physical hazard in a food product. These range from natural sources such as rocks, wood, or product components such as shells or bones, to processing components such as metal shavings, equipment parts, or glass pieces from packaging materials. Other potential foreign materials can also be introduced to the finished product at many stages throughout the production of the food such as broken light bulbs, operator contamination, or pest contamination. Ensuring a product is safe from physical hazards, it is generally completed by multiple steps throughout the production process with added attention at Critical Control Points.

Various programs such as pest control programs, good manufacturing programs, foreign material control, receiving and material control programs, and various other programs help lay the foundation for ensuring no physical contamination occurs. In this article, we shall be reviewing a few existing methods that are currently used to control foreign material as well as some relatively modern innovative technologies that may be implemented.

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From RASFF, Canadian Food Inspection Agency, and Food Drug Administration, it was possible to obtain information regarding different foreign bodies.

Foreign bodies reported by Food Drug Administration (USA):

Food Drug Administration

Foreign bodies reported by Canadian Food Inspection Agency:

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Foreign bodies reported by RASFF (European Union):

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In Europe, records show an increase in the tendency for notifications in plastic, glass and metal, but a reduction in “other physical contaminants”. On average, 54% of the “other physical contaminants” were insects. The reduction of this occurrence was the main reason for the reduction in tendency of “other physical contaminants”. In fact, the presence of insects started as 36 % of all the foreign bodies’ notifications in 2015, but soon decreased down to 10% by 2018.

It can be clearly noticed that in Canada, on average, metal, glass and plastic together were only 44% of the notifications. But, contrary to Europe, the percentage of insects on the “other physical contaminants” has been increasing from 29% in 2014 to above 67% in 2017& 2018.

Screening and Filtering

As some products cannot support a wash step other physical separation methods such as screening or filtration can be used to remove foreign material. These screens can separate solid foreign materials from liquid products or separate solid items based on size. Some systems require mechanical agitation or movement to allow for more effective product flow but the basic method is creating a physical barrier that removes as much foreign material as possible.

Flour is used as a raw ingredient in many food products and therefore it is critical to ensure that suitable physical screens are in place to safeguard the quality of the final product. Whether it is a small artisan bakery or a large industrial flour mill, the compact sieve (screen) is able to handle very large capacities of all flour types including hard wheat, soft wheat, semolina, corn flour and many more. The compact screen can be installed under the bulk silo to safely screen flour on receival from a tanker or rail car to ensure that small rock, stones, plant and other large foreign matter does not enter the silo. These screens or filters will wear and break eventually and must be inspected and replaced before they become a source of contamination and introduce metal themselves into the system. These systems are effective in removing many hazards and foreign materials but can still fail, create contamination, and cannot stop downstream contamination. For these reasons additional steps may be needed for even further control of foreign materials.

Detection and Removal of Metal Contaminants


Another method of physical foreign material removal is the removal of ferrous metal through the use of various types of magnets. Magnets are the most basic level of metal removal used in the food industry. The prevention of metal contamination in food has long been of importance to the food manufacturing/packing industry. Often these are used to help protect machinery and help identify any downstream equipment failure. During production process, metal parts can enter the food products such as baby food, fruit juice, frozen or canned vegetables, spices, flours, sauces, grain, powdered milk, sugar or chocolate to name just a few. This can cause costly production interruptions, damage claims and product recalls. To prevent this, many leaders in the magnetic industry have developed new innovative ways to combat these issues.

Magnets can remove ferrous materials, whereas rare-earth magnets can also remove magnetic stainless metals as well as weakly magnetic materials. Magnets can also be employed to safely control the points downstream, in order to remove metal prior to packaging.

The advantage of using magnets as a metal removal option is that they can remove many particles, including metal dust and pieces too small for identification by other methods, with very little maintenance, cost, or product loss. Magnetic filters are generally located in the product flow and can filter out the smallest Fe particles down to 30 microns and weakly magnetic particles (stainless steel residue). These extremely fine Fe and stainless steel particles are so small that they cannot even be detected with a metal detector. These magnetic filters ensure that it can capture very small ferromagnetic particles from 7 – 30 microns and ferromagnetic dust. It generates a magnetic field of 10,000 – 11,000 Gauss (+/-5%).

Metal Detectors

Most common of foreign material within grain and milling processing is metal. Successful detection and separation of metal will protect processing equipment from damage, and prevent safety hazards from consumers.

Many facilities implement metal detectors for removal of hazardous non-magnetic and magnetic metal foreign materials as well as a final check of packaged product to verify product safety. Even with the most robust metal detection controls, metal contamination of food still occurs. If we take a close look at food manufacturing processes, we observe many unit operations involving the use of metal materials such as cutting, slicing, crushing, sieving, mixing, pumping, packing etc. Metal is the standard fabrication material used in machinery, utensils and handling equipment.

Over the years, food standards and retailers have developed requirements which demand food businesses to adopt a series of control and detection, which the food company can offer the consumers as the best level of protection. These controls typically take the form of inspection, checking, detection system and removal of potential metal hazards.

Metal detectors have advanced greatly in their abilities to detect metal and to do so with high efficiency. The basic operation occurs by a balanced coil system using electromagnetic induction or by magnetic field systems.

In basic balanced coil systems, there are three coils, one transmitting coil and two receiving coils. When an item is placed through the transmitting coil and contains metal, the metal will disrupt the magnetic field that is created by the transmitting coil.

The detectors can identify changes in the amplitude and phase of the current caused by metal entering the detection field. This causes the metal detector to trip and remove the metal from the product flow. These systems can be limited in detection capabilities due to the material that is being tested and the type of metal that is targeted. Materials that have higher conductivity levels, usually due to salt or moisture, can be more difficult to identify metal using balanced coil systems. Magnetic field detectors have a strong magnetic field that can identify magnetic metal inside of aluminum cans and is used solely for identifying metal inside of already sealed cans. Other aspects of metal detection improvements include; operation in various environmental conditions such as heat, vibration and moisture and the reduction of cross signal effect from machinery or communication equipment.

If metal is the only hazard or quality concern present for a facility, then these may be effective in controlling the facilities’ risks. However, if a process has other inherent risks or a facility wishes to identify other non-magnetic foreign materials, additional or alternative methods must be implemented to ensure product safety and quality.

X- Ray in Food Inspection

Emerging issues such as fraud and the intentional contamination of food have also highlighted the importance of food inspection technology. The operation of food safety management systems incorporates the principles of Hazard Analysis and Critical Control Points (HACCP); inspection forms a key part of procedures designed to control potential hazards. The role of technology for inspection purposes has become increasingly important due to the ever-increasing emphasis by consumers and regulatory authorities on food safety and quality.

X-rays are a form of invisible electromagnetic energy with short wavelengths and high energies. The use of X-ray technology is most familiar to people through its use in medical imaging. However, X-rays can also penetrate food products and allow the imaging of the internal features of the food to detect physical defects or contaminants without damaging the food product.

As an X-ray enters food, it loses some of its electromagnetic energy. If the X-ray encounters a dense area in the food, such as a metal contaminant this will reduce the X-ray energy further. As the X-ray leaves the food, a sensor in the inspection equipment converts the X-ray into a greyscale image of the foods interior. The denser a contaminant, the darker it will appear in the image, which helps in its’ identification.

Uses of X-Ray Inspection

Depending on the type of X-ray inspection equipment and the nature of the food product, X-ray inspection can identify a variety of physical contaminants including metal, glass, rubber, stone and some plastics. Because X-ray inspection provides non-destructive imaging, it’s use has become more widespread for packaged processed foods, particularly those in bottles, cans, jars and pouches. Increasingly, as the technology advances X-ray inspection is being used for in-line production control and verification.

Considerable research has highlighted the potential of X-ray inspection for the grading of fruits, vegetables and grains, and detection of bones in chicken and fish.

Some advanced X-ray inspection systems can simultaneously perform in-line quality checks detecting physical defects, measuring mass, counting components, identifying missing or broken products, monitoring fill levels and inspecting the seal integrity of packaging. As such, X-ray inspection systems may help reduce inspection costs for some food businesses.

As the capability of X-ray inspection to detect contaminants is directly related to the density of the product and the contaminant, there are some contaminants which X-ray inspection systems have difficulty in detecting and imaging. These include hair, paper/cardboard, low density plastics and stone, string, wood and soft bone tissue such as cartilage. However, advances in X-ray inspection technology and particularly coupling of other technologies to improve imaging are addressing some of these limitations.

Ultrasonic Imaging

Ultrasonic imaging is another potential method for foreign material identification and uses the application of a 20 kHz or larger sound waves to a product, and then detecting the resonating frequencies of materials or the measurement of sound.

Impedance or time of sound transfer through the material to identify any hazards that are present. Methods such as metal detector, X-ray or ultrasonic imaging have the advantage of being nondestructive and do not negatively affect the tested product. They also have the advantage of being applicable to multiple products and be cost effective.

Previous testing has shown more effectiveness in areas when product is transported through water such as a produce facility where water flumes are employed. But recent studies have shown the ability to detect differences without contacting the material or the need for a conductive medium. Other potential avenues for this method include detection of foreign materials in canned products. These have been able to identify foreign objects in cans as small as 1mm in length but can be negatively affected by container shape and irregularities. Further development will need to be made if these units are to become used more commonly in the food industry.

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The collection and production of food products lead to the possibility to contaminate food at many steps throughout the process. With the globalization of the food system, this process continues to grow in size and in geographic distance. Foreign material can come from the fields, factories, producers, or during the transport or storage of products. Inadequate removal of foreign materials can lead to potential consumer safety concerns, quality concerns, or product recalls. All of which can be costly and detrimental to the image of a company. Therefore, cost effective means are needed to remove these potential risks and reduce their potential to reach a consumer as much as possible. The statistics from four different global authorities have shown that there is no clear tendency of these occurrences from slowing down in the last 4 years, so the industry must proceed with the efforts to improve the management of foreign bodies.

Traditional methods such as magnets and metal detectors are still the common methods throughout the food industry. As new methods such as X-ray inspection and ultrasonic imaging improve and become more economically feasible, they may become prevalent in the food industry and continue to drive towards safer, higher quality food products. In the following table some characteristics of the diferente methods are summarised.

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Nuno F. Soares, Ph.D., is an author, consultant, and trainer in food safety. He his a Food Engineer Specialist and senior member of the Portuguese Engineering Professional Association. He has over 20 years of experience in food industry as quality and plant manager. His latest book is “ISO 22000:2018 Explained in 25 Diagrams.”  

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This article was published with the permission of Nuno F. Soares and the Original Article can be read here: