* Anurag Mishra

The biggest reason for buying packaged food by any consumer is ‘to have safe experience ‘ and if there happens to be anything which is not expected in the pack ,

there will be increase in the risk of consumer dissatisfaction,  regulatory risk and at the end it may damage the Brand Image .

This may lead to recall of the product and there are many examples available in the market. Food recall can happen due to a variety of reasons, including the detection of  physical hazard in food products.

Foreign matter or Physical hazard is any physical stuff which is not expected by consumer in the pack or anything other than declared by the manufacturer on the label; glass , wood , metal part,  plastics , rubber , threads, stone etc comes under the physical hazard and all these must be avoided at every point of processing

( farm to fork or Grass to Glass ) .

A total of 42 physical hazard related recalls were issued in the U.S. in 2017, with metal and plastic contamination topping the list in this category. Each accounted for 12 and 11 total recalls, respectively. Almost all of these recalls were for various meat products, including one issued by poultry giant Perdue Foods. 

In 2017 a global confectionery giant recalled whooping amount of its products globally because of possible physical hazard in the products .

To avoid above issues, manufacturers must deploy suitable mechanism to detect and eliminate any possible physical hazard in the finished goods. Selection of the mechanism must be based out of basis risk assessment and type of possible foreign object in the entire process.

Development in  modern technology has given some robust options to detect and eliminate foreign objects from finished / semi finished goods. In recent years these options seems to be very effective and are used across the globe. Some of the available and effective options are:

Magnets :

Magnets are used widely in the food manufacturing facility in between the process. As Magnets do not detect the hazards real time and with 100% accuracy so most of the time its used in up stream processes to minimize the hazards in final product.  Ideal strength of the magnet should be more than 10000 gauss and all the magnets must be calibrated minimum once in a year ( externally ) . Generally metal detectors are installed after magnets to minimize the hazard to the acceptable level . 

Metal detectors

Metal detectors are the most common and widely used method to detect the metallic physical hazard in the food industry, but as the examples above demonstrated they cannot control a large spectrum of non-metal materials. When using this type of equipment, metal objects within a food product, produce an unbalance in a balanced radio frequency or magnetic field. This typically generates an electrical signal alerting the equipment operator of the situation.

This method can detect very thin metallic objects such as metal rust and aluminum foil. However, certain factors can affect the sensitivity of metal detectors. The type, shape and orientation of metal play a  big role in the effectiveness of detection. The equipment’s operating frequency also affects the sensitivity. Other factors like position of metal in the aperture, type of product scanned, packaging material and environmental conditions such as vibration are often referred as limitations to appropriate detection. Also, non-metallic contaminants, such as rubber,  glass etc , are not detectable since they do not affect the magnetic field.

Metal detectors are easy to operate, typically have low maintenance costs and are cheaper than other alternatives like X-ray detection. Thus they can be used almost anywhere in food industry facilities. A metal detector placed at the end of a production line, as the last barrier to guarantee that metal contaminants do not reach the consumer, is an obvious move. Nevertheless, food safety professionals should also consider that if that detector (or a second one) is placed at the beginning of the line it could have extra benefits.

Because of its operational challenges , metal detectors must be verified with standard test pieces frequently ( hourly verification is better ) and health check up of detector must be done by OEM once in a year . 


In the case of X-ray detection, the equipment produces an image of the food product that can be analyzed for contamination. Due to their high energy, X-rays can penetrate solid bodies. When going through the inspected product X-rays are more or less attenuated according to the density of matter present. If an object is present with a different density from that of the food product, it will be represented in the image (picture below, on the left and middle). The ability of spotting different densities adds another feature to the equipment – the capacity to identify product defects like missing products in packages (picture below, on the right), products without filling or incorrect shape .

X-ray systems can detect several foreign bodies such as metals, non-ferrous metals, stones, glass, PVC plastic, bones, ceramic, Teflon plastic, sugar or flavor clumps. On the other hand, X-ray machines cannot detect some contaminants such as paper, cardboard, wood, hair, insects, thin glass, low-density plastics and low-density stones. One interesting application is in the seafood industry to detect fish bones. There are available equipment based on this technology that are prepared to detect needles (injected fish products) and calcified bones (according with the manufacturer “commonly achieves a 99% detection rate on calcified bones larger than 0,7 mm, in their smallest dimension, with false positives at or below 3%”).


Ultrasound-based measurement is a promising method to detect foreign bodies because it has the ability to differentiate discontinuities in acoustic impedance between different regions within a given volume. These discontinuities would represent something that differs from its surroundings, such as a foreign body. This technique, although already used widely in the food industry in liquid level detection or suspended solids concentration (among other applications), is still not well known as an option for foreign body detection. Despite that, for instance, a patent has been conceded in 2004 for an ultrasound transmitter that detects foreign material in heterogeneous process streams, like bones in a slurry of chicken meat. In the case where pulse and echo mode is used for measurements, the transducer transmits impulse ultrasound signals to the food product and the ultrasound velocity is calculated by the echo’s round-trip and time elapsed. Flaws and particles in the food product are detected by examining either the reflected signal amplitude or arrival time due to impedance discontinuity. Several advantages are linked with ultrasound technique, since it has a large applicability, most materials can be detected, and the equipment is low-cost and performs truly nondestructive tests.

By using above options we may eliminate the foreign objects in  products so that the consumer gets the best experience and value for money.  

*Group Head Quality Assurance and Food Safety – Wilmar ( India )