Foreign object detection and food safety – in search of the blue glove

Slivers of glass in fruit juice or baby food, metal shavings due to machine wear in mince, plastic fragments from damaged packaging materials in chocolate bars, little stones and wood splinters in unprocessed food such as grain or vegetables – no consumer wants contaminated products to end up on their plate or in their glass.

If foreign objects are not detected, the consequences are sometimes unpleasant and often dangerous. Injuries to the mouth, throat or gastrointestinal tract, infections and allergies are possible outcomes. Microplastics can accumulate in various organs and may cause inflammation or even long-term damage to the cells.

Metal threads and fragments are some of the most common types of contaminants in food. Some foods have a high risk of being contaminated with metal parts, for example pata negra, an expensive Spanish ham. “The livestock live outside and are therefore also exposed to ricochets from hunters”, explains Johannes von Stein, Vice President Sales Food at Sesotec, a systems specialist for industrial foreign object detection. “None of the ham producers want to chase away customers who are willing to purchase a ham that costs up to 1,000 euros.”

In addition to special sieves, food producers rely on magnet and metal detectors and X-ray systems to detect and remove foreign objects. “A combination of different systems is ideal”, explains the expert von Stein. Magnet systems are especially suited to product lines where iron particles like nails, screws or metal shavings may be present. These contaminants are more likely to occur in the production of bulk goods such as spices or cocoa powder. “The most cost-effective and generally mandated variant of foreign object detection is the metal detector”, says von Stein. “It can detect contamination from stainless steel or aluminium, where magnets would fail.”

X-ray inspection systems are being used increasingly for organic products with particularly strict quality requirements. They are ideal when there is a chance of foreign objects made of glass and ceramics or larger pieces of bone ending up in the production line – for example when filling glass jars or processing jams or meat.

End-of-line product inspection is an essential part of any industrial production line. It is designed to ensure that all packaged products are free from contamination for their further progress along the supply chain. “But it’s not enough to rely on this alone”, says food inspection expert von Stein. “Contaminated raw materials can get into the manufacturing process at every point of the production line. Human error also plays a major role here. For instance, the blue gloves often worn at production lines repeatedly end up in the manufacturing process.”

On their way through the production lines, contaminants – a screw, for example – can be broken up into small pieces during the various process steps. This creates more and smaller foreign objects that become increasingly hard to detect. “The later I separate them out, the higher the costs, for example due to the energy, ingredients, packaging trays or films that have already been used. The risk for further damage or necessary machine downtimes also increases”, the process expert summarizes further risk factors.

The sooner checks are carried out and the more regular they are, the better. Ideally, all critical checkpoints in processing are defined and equipped with modern detection systems. This prevents large quantities of food having to be separated out at a late stage and sent for manual inspection, which is time-consuming. Sometimes large quantities of edible food are disposed of for safety reasons, even though only a single product may be contaminated. “It’s a positive side effect of early monitoring”, says von Stein. “In this way, a supplier’s product quality is already checked when the goods are received.”

For metal detection, Sesotec uses artificial intelligence to complete particularly challenging tasks. For example in the production of Parma ham, which contains a great deal of salt. Shot pellets and salt share a number of physical properties. They both conduct electricity and emit similar signals when their electrical conductivity is measured. This means that the salt in the ham could be falsely detected as a shot pellet.

“To solve this problem, the monitoring device works with different frequencies that allow us to suppress the signal emitted by salt so that only genuine foreign objects such as shot pellets are recognised”, explains the manager. Thanks to this special setting, the ham remains in the production flow and is not mistakenly ejected, which ensures greater monitoring precision and efficiency, as well as less food waste.

“Modern AI systems have the great advantage of being trainable”, says von Stein. “With the help of large amounts of sample data, they can learn to distinguish between different signals.” Over time, the AI identifies different patterns and properties to distinguish salt from shot pellets or typical foreign objects such as fragments of glass, metal threads or wood shavings. “The system therefore recognises foreign bodies more and more reliably over time and reduces false-positive rejects.”

Sesotec’s Integrated Compliance Monitoring is a self-monitoring safety system. During production, food is fed through a metal detector at defined intervals, which continuously generates an electromagnetic field. Foreign objects like metals affect this field due to their specific electrical and magnetic properties that differ from the surrounding materials, thus triggering a reaction.

The regular signals ensure that the system is correctly calibrated. The message “I’m ready for operation” is transmitted continuously. If an alarm is triggered, only a small quantity of food has to be sent to quarantine for further inspection. This means that only the affected batch is stopped, while the rest of the product can safely continue to pass through the inspection.

“Today, modern lines produce packaging units at speeds of 300 to 900 per minute. In the beverage sector, this figure jumps to 2,000 cans in 60 seconds. Fully automated monitoring is absolutely essential for effective quality assurance here”, says von Stein.

“Quality is non-negotiable”, says von Stein. “More and more consumers are paying close attention and are well-informed. Nowadays, quality and food safety are vital factors for consumer confidence and ultimately for economic success.”

Every food producer is aware of the strict legal requirements laid down by the EU and many other countries. Infringements of these can lead to expensive recall campaigns, fines and, in the worst case, legal proceedings. According to an analysis of food safety alerts in the EU, around 12 to 15 percent of all food recalls in recent years have been triggered by foreign objects. In the wake of these alerts, millions of tons of food are destroyed for safety reasons.

Implementing monitoring measures and investing in modern safety systems is worthwhile, as recall campaigns are time-consuming and incur high costs of 1.31 million euros on average according to studies carried out by insurance companies specializing in recall and product liability insurance. In the food sector, the average costs are said to be even higher, as particularly strict safety standards apply here. The reputational damage for affected companies often lasts years and entails long-term economic losses.

“With our complex systems, we focus on a comprehensive view of quality management. This makes all production stages transparent for our customers and provides them with reliable data for the necessary documentation”, says von Stein.

Innovative technology helps manufacturers comply with strict food safety regulations. However, aside from all the ethical arguments, business decisions are often determined by economic aspects that can turn a duty into a pleasure. This requires the interlinking of expertise from different fields in order to facilitate the implementation of progress in practice.

Sesotec is a member of the SAVE FOOD initiative, and Johannes von Stein explains why: “In industrial nations, almost a fifth of all food is wasted during manufacturing and production. Finding solutions to prevent food waste is our passion. We appreciate the SAVE FOOD platform because we can meet strong partners here. Food safety will only truly be practised once it is profitable. That’s what we want to work towards together with others.”