The role of metal detectors in food safety

The United Kingdom's highly mechanised commercial food processing industry is fast and efficient. It delivers a wide range of wholesome foods, including dried, canned and bottled ingredients, to retail outlets throughout Britain and abroad.

Industrial food processing involves multiple techniques performed by many different types of machinery. Ingredients are constantly in contact with metal implements such as blades, conveyor belts and sealing equipment.

Although the machinery is usually dependable and robust, the potential for metal contamination remains. Therefore, reliable metal detectors are a vital part of commercial food processing. They alert production lines to metal contamination before the products are distributed. Metal detection machinery enables food processing factories and retailers to present the public with foods that are safe and trustworthy.

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How Widespread is Food Contamination?

As of 2020, there were around 1,685 manufacturing plants in the UK. The food and drinks manufacturing industry contributed approximately £30bn to the UK economy in 2021. According to the Government's statistics, 93% of consumers trust food that's processed in the UK is perfectly safe to eat. However, contamination from various sources can occur at any stage. Hygiene regimes or bacterial contamination may pose a problem if routines are not strictly adhered to.

In 2021, 106 incidents were reported concerning foreign bodies being found in food. Some of these may have included plastic, aluminium foil or glass. However, metal contamination is a prime concern due to the high use of metals in the complex production lines and in the canning process.

In 2022, one major incident involving fragments of metal occurred in a whey protein product sold by Tesco, one of the UK's leading supermarkets. However, the relatively low number of cases involving food contaminated by metal is due to the efficiency of sophisticated metal detecting machines.

What Types of Metal Contaminate Food?

There are generally three types of metal that may contaminate food while it is being processed. Some of the metal could be fragments splintering away from equipment, or from problems that occur during processes such as sealing tins of food. Other metal contamination could be due to poor safety measures during routine maintenance or the repair of equipment such as conveyor systems.

Ferrous Metals

These are usually steel alloys containing iron. They are the easiest type of metals to locate as they are highly magnetic and conductive. Ferrous steel is commonly used in the manufacture of heavy-duty machinery for food production lines.

Non-Ferrous Metals

These metals include aluminium and tin which are widely used for containing foods. They are not magnetic and therefore more difficult to locate. However, non-ferrous metals are highly conductive enabling sophisticated metal detecting machines to locate their presence.

Stainless Steel

This metal contains chromium which provides it with anti-corrosive properties. As such it is usually used for equipment such as blades and dough kneading hooks. Stainless steel is non-magnetic and has low conductivity making it particularly difficult to detect. Foods with a high moisture or salt content often contribute to obscuring its presence. However, technologically advanced machines are usually capable of locating stainless steel debris.

Are Metal Detectors Used at any Stage of Food Production?

Metal detecting equipment is frequently stationed at Critical Control Points (CCP). These are usually breaks between the different procedures that occur throughout food processing routines.

For instance, baked beans undergo several different procedures, beginning with blanching the dried haricot beans with steam. They are then soaked at least once to rehydrate them before they are added to a rich, lightly spiced tomato sauce. The mixture is poured into metal tins, which are then sealed and cooked under high pressure.

Baked beans are in high demand as they are the most popular processed food in the United Kingdom. In fact, more baked beans are consumed in Britain than in any other country. According to the Guinness Book of Records, Britons enjoy 11 pounds 10 ounces or 5.3 kilograms of baked beans per capita every year.

To satisfy the demand for producing more than 1.5 million tins per day, the processing of baked beans has been refined to a two-hour procedure. Conveyor belts transport the beans at up to five miles per hour. Metal detecting machines are highly proficient at dealing with the intensity of such speeds at any stage of the procedure.

Metal Detecting Machinery Used in Food Processing

Food metal detecting equipment manufactured is specifically designed for the food industry. The machines are precision engineered to the highest specifications, making them highly reliable and efficient. They are also compliant with current legislation regarding food safety. In addition, machines can be custom-built to suit individual food processing requirements.

Independent, stand alone metal detectors offer versatility as they can be placed at any CCP throughout the food processing procedure. They can also be used as a final end-of-procedure safeguard, screening finished containers for pieces of metal.

Typical package sizes when detecting fragments of metal often range from 120 millimetres to 400 millimetres. Sensitivity refers to the type of metal that can be detected. FoodMC.co.uk has machines capable of detecting ferrous metals (FE) from around 0.8 to 1 millimetre. Stainless steel, the most difficult metal to detect, can be located from sizes ranging between 1 millimetre and 3 millimetres.

Additional features include touch screen control pads that are easy to use. The menus are shown in full colour and are very intuitive to navigate. Operators can also program in new products without having to rely on the expertise of an engineer.

For coordinated results, the metal detecting machines can be used in conjunction with checkweighers. These chain belt system machines confirm packages are the correct weight. They generally operate at around 30 metres per minute and within a range of between 5 grams and 3,000 grams. The checkweighers also include a choice of reject mechanisms such as pushers, sliders and air blowers.

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How Food Metal Detectors Work

Metal detectors for food are usually placed at vital CCPs where contamination can be readily located. Food processing systems usually include extensive roller conveyors with a variety of mechanisms such as gravity feed or vertical fall.

Liquids are usually pumped through a pipeline. Modern metal detectors for food have evolved a great deal since their development in 1948. They are driven by sophisticated microprocessors that provide the highest level of accuracy.

Generally, metal detectors in the food industry operate through a balanced coil system that is shielded by an outer casing. The aperture through which food or packages pass contains two enclosed coils; a receiver coil and a transmitter coil.

They create a magnetic field that identifies metal particles in a process known as illuminating. The reject mechanism then propels the suspected package into a lockable container to prevent it being accidentally returned to the production line.

How Metal is Detected in Food

The search heads of commercial food metal detectors usually contain multi-scanning technology. They operate with at least twice the accuracy of models manufactured in the pre-computerised era. Systems that use multi-spectrum X-ray scanners are regarded as perfectly safe for the working environment as they don't use live radiation. This type of metal detector passes a computerised beam through the food and its container to create an on-screen image.

If a metal particle is detected, the system automatically rejects the container and food. Metal detectors carrying liquids or foods through pipelines usually include an audio alert. The system is ideal for checking foods contained in aluminium or tin cans. It can locate non-ferrous metals, and other contaminants such as rubber and plastic. An alternative solution for products destined to be wrapped in foil is to check the food before it is packaged.

The sensitivity of the search head should be a suitable match for the food it is checking. Some search heads detect large pieces of metal and are usually placed at a strategic CCP early on in the mechanised conveyor system. This prevents bulky contaminants infiltrating further down the system where the machinery may be more susceptible to damage. Metal detectors placed at later intervals may have increased sensitivity and be suitable for locating minute metallic particles.

Safety Guidelines

Commercial food processing carries enormous responsibility in maintaining safety standards in order to protect the consumer.

Food Machinery Company metal detectors for food processing comply with current government health and safety standards such as BS/EC 852/2004 and BS/EC 853/2004. However, it is important to adhere to a rigorous code of practice when operating metal detectors for food. Detailed records must be kept regarding the source of all the ingredients included in food processing. Computerised systems should be locked and protected by strong passwords. They should only be accessible to authorised personnel.

Avoiding False Readings

Metal detection machines contain highly sensitive components that can be affected by a number of conditions. To prevent false readings, the CCPs where metal detectors are positioned should be chosen with care. Try to avoid points along the production line where the machines could be affected by heavy vibrations. They also need to be placed out of reach of any electromagnetic interference from cables and electrical equipment.

The delicate mechanism of the metal detector's coils can be affected if foods are constantly changing temperature. This could be through cooling down from being heated, or if frozen products begin to thaw. High levels of salt can also cause fluctuations in the readings. Sensitivity adjustments can compensate for the discrepancies. Alternatively, a multiple search head can be programmed to compensate for minor variations.

Safety Tests

Metal detecting machines require a scrupulous maintenance regime to ensure safety guidelines are met at all times. Food metal detectors must be tested for accuracy at the start and end of each shift. They should also be tested every hour and whenever a different product is introduced to the production line. The metal detectors should be tested first with a safe, metal-free package, followed by one that includes appropriate metal pieces.

Some machines are supplied with specialised plastic strips fitted with metal. Conducting frequent tests ensures that if metal is discovered, a minimal amount of food is affected. It should be easily traced, preferably before it has left the factory.

Routine Maintenance

The machinery used in commercial food processing is heavy duty and designed for the stresses of a demanding regime. However, it is still constantly suffering wear and tear, particularly from the effects of relentless vibration. Routine maintenance should be carried out at planned, regular intervals. This prevents expensive downtime occurring through unexpected machine failure.

Replacement screws and rivets should be containerised and accounted for during repairs. Any work involving soldering, drilling or welding must be carried out off site.

What to Do if Your Product is Contaminated

When metal contamination of food occurs, swift action must be taken to minimise the impact on public health and safety. Hourly testing of metal detectors helps reduce the size of a batch, making the contamination easier to locate.

The affected batches could be tested again after additional tests have been made to account for false readings. In some instances, a consignment of food suspected of contamination may have already reached the retailer.

In spite of the detrimental effect advertising the hazard may have on a company's reputation, the product must be recalled immediately.

An Essential Process in Food Production

Metal detecting and checkweighing are essential processes in food production, and are necessary to ensure the safety of food before it leaves a facility.

Reliable metal detectors for food processing are clearly successful in locating metallic fragments. The Food Machinery Company has been supplying highly efficient food metal detecting machines for fifty years. Our machines can be tailored to any food production process, helping to keep production lines safe and hazard free.