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An 8-step guide to metal detecting in the food industry and why it’s so important

Increasingly speedy production lines have revolutionised the food processing and pharmaceutical sectors, helping manufacturers to cut costs and maximise profit margins.

While this is excellent news for the industry, speed should never be prioritised over food safety. To avoid this happening, you need an efficient and accurate metal detector in food processing has never been more critical.

There were three notable metal-related scares in 2017. Tesco had to issue an urgent product recall when there were fears that Quorn Meat-Free Mince was contaminated with fragments of metal. Lotus Bakeries UK recalled Lotus Biscoff Crunchy Biscuit Spread because the product may have contained small pieces of metal. Morrisons had a crisis on its hands when metal wire was found in fresh green beans.

In each instance, the cost of recalling the product was significant, with added reputational damage. Years spent building up a trusted brand can be wiped away in a moment if products must be recalled and customers take to social media to complain about safety fears. If the issue flares up into mainstream media, you’ll have a full-on crisis to deal with.

Given the financial and reputational costs involved, food processing and pharmaceutical companies must invest in robust metal detection systems, to protect the company and consumers, avoid product recalls, safeguard reputation and secure revenues.

When it comes to contaminants, metal is one of the most common in the food processing industry. It can enter the production line at any point because metal is the most commonly used material in the construction of machinery, handling equipment and various specialist utensils.

While any good metal control programme should start with prevention rather than detection, the installation of detection equipment is critical to ensuring that even the tiniest scrap of metal does not enter the food or medicines we ingest.

This guide will discuss the types of metallic contaminants companies need to detect, the range of detectors that are available and where they should be placed – as well as the challenges you may face along the way.

Here’s a list of the subjects we will cover in this guide:

What types of metal contaminant are there?

Typically, there are three types of metal a detector can sense. It’s important to understand the differences as this will be one of the factors determining the type of detector you need.

The three metal types are ferrous, non-ferrous and stainless steel.

  • Ferrous metals – high in iron. These types of contaminants are both magnetic and conductive, which means they are easily sensed by standard metal detectors.
  • Non-ferrous metals – do not contain appreciable amounts of iron. Although non-ferrous metals are not magnetic, the fact they are conductive means that they too can be easily detected with the right detection equipment, properly installed.
  • Stainless steel – generally considered a ferrous metal, but one that is high in chromium. It is the most difficult to detect as it is neither magnetic nor conductive. Stainless steel is even more difficult to find when the product contains water or has a high salt content.

Inspection and detection challenges

Metal detection equipment is not always sensitive enough to avoid false triggering – which may result in needless waste, slow down production and ultimately weigh down profits. Standard metal detectors may struggle to detect metals accurately and consistently on production lines. This is because different products give off varying signals according to, for instance, the differing moisture content of products – known as the product effect. This issue can be overcome with the use of multispectral x-ray detectors.

The need to drive maximum efficiency, while at the same time maintaining robust metal detection systems, is another challenge. No manufacturer wants to slow down their food production lines. Still, they need to balance the need for efficiency with the necessity to detect food hazards and avoid costly product recalls and reputational damage.

Complying with regulatory requirements can also pose a risk. In a competitive industry governed by strict standards, regulations and legislation, inspection devices sit at the heart of any well-designed, safe production process. In the UK, you need to comply with Food Standards Agency and British Retail Consortium Global Standards (BRGS), the Groceries Supply Code of Practice (GSCOP), as well as EU directives and global standards such as the Global Food Safety Initiative. You should also check out local laws and any requirements relevant to the sector you operate within, such as HACCP (Hazard Analysis and Critical Control Points) and GMP (Good Manufacturing Practice).

Operator safety is of utmost importance. Accidents are traumatic for the individual/s involved and their families, as well as their colleagues. They invariably result in downtime, and if the news gets into the public domain there are reputational risks.

To protect operators, attention must be paid to every detail of the design of the metal detection system you choose. When considering which metal detection system to go for, think about whether it has shatterproof round-edge guards, safety valves and guarded in-feed and out-feed rollers that remove the risk of finger traps. You also need to provide the correct training. It is vital for operator safety that people using the machinery know how to do so in accordance with manufacturer instructions.

How do food metal detectors work?

Metal detectors have come a long way, now utilising multiscanning technology, which has revolutionised the identification of metal in the food production and pharmaceutical industries. Multiscanners can detect metal contaminants that are as much as 50% smaller in volume than previous detection systems, including food items with high product effect such as water or salt content.

With multiscan technology, it is possible to scan up to five adjustable frequencies, raising the probability of detection. Multispectrum x-ray systems use a computer to detect metal and other contaminants in food processing. They do this by passing a beam through a product, which bounces back to the computer to create an image. The on-board control system then decides whether the product should be accepted or rejected based on its analysis. The software used in the control system accepts or rejects the image (and the item it’s showing) based on a company’s pre-determined acceptance standard.

If you are concerned about any health issues surrounding the use of x-rays, you needn’t be. Modern x-ray systems for food and pharmaceutical applications don’t contain sources of live radiation, such as uranium; in fact, they are designed to provide a perfectly safe working environment for operators. Provided safety guidelines are followed, there are no restrictions for anyone, including pregnant women and young adults operating this type of equipment.

Which metal detector is best for me?

If cost is your overriding consideration, standard metal detection may seem the most suitable solution.

However, product safety decisions are rarely that simple. The performance of each solution is affected by factors such as the size of the product to be inspected and product effect – plus it’s important to compare lifetime costs, not just the upfront capital costs. The type of product and the likely contaminants will also affect the choice.

Sometimes, the answer is to install more than one detection system at different Critical Control Points (CCPs) on the same production line. For example, a metal detector or a bulk flow x-ray inspection system placed early in the processing line can remove large metal or non-metallic contaminants before they reach delicate machinery downstream. This is important, because if these contaminants are not detected, they could damage the machine or become fragmented into multiple, smaller, more difficult to detect contaminants.

As well as protecting the machinery, the inspection equipment will remove contaminants before further processing increases the cost of product waste.

Metal detection and x-ray inspection offer different capabilities. To assess those capabilities fully, the first step is to carry out a Hazard Analysis and Critical Control Points (HACCP) audit.

Your HACCP audit will identify the risks of contamination being introduced into the manufacturing process, and the types of contaminants likely to be encountered. CCPs should be established to mitigate the risks and establish where product inspection equipment needs to be installed.

If the HACCP audit determines that metal is likely to be the only contaminant found, then a metal detector is likely to provide the most cost-effective solution. However, we strongly advise that, due to factors such as packaging type and product effect, all food processing firms perform a product test to establish the most suitable technology.

If other contaminants like glass, mineral stone, calcified bone or high-density plastics and rubber are identified as likely to be encountered, then x-ray is the best option.

While it is usually the case that there’s only one suitable solution – either metal detection or x-ray inspection – there are occasions when it may be necessary to install both metal detection and x-ray inspection at different CCPs on the same production line.

Modern metal detectors can identify all metals, including ferrous (chrome, steel), non-ferrous (brass, aluminium), as well as both magnetic and non-magnetic stainless steels in food and pharmaceutical products.

X-ray systems go a step further by offering the capability to detect metal, as well as non-metallic contaminants such as glass, mineral stone, calcified bone, high-density plastics and rubber compounds. They can also simultaneously perform a wide range of in-line quality checks such as:

  •  Measuring mass
  •  Counting components
  •  Identifying missing or broken products
  •  Monitoring fill levels
  •  Measuring headspace
  •  Inspecting seal integrity
  •  Checking for damaged product and packaging

Five types of metal detector are commonly used in the food processing industry.

  1. Checkweigher combination systems – this solution is ideal for manufacturers supplying a variety of products to the big supermarkets, to ensure compliance with the grocers’ requirements and regulatory stipulations. Checkweigher combination systems come in different sizes, typically the full-size combination system and the slim line combination system. Systems must conform to HACCP, retailers’ Codes of Practices (COPs) and British Retail Consortium criteria as detailed above.
  2. Conveyor based systems – these are frequently used for the inspection of fruits, vegetables, cereals, meats, yoghurt and bread.
  3. Pipeline for pumped products – the most common application is for beverages, sauces, soups and dairy.
  4. Vertical fall or gravity feed – used in the processing of powders, grains and granules.
  5. X-ray machines – these are typically used to detect foreign bodies that standard metal detectors cannot, such as plastic, rubber and glass. X-ray systems are also capable of screening products that are packed in metallic casing such as foil, metallic film or aluminium. Traditional metal detectors do not have this capability.

However, x-ray technology is not a ‘magic box’. It will not detect contaminants with very low densities such as wood, insects or hair.

Whichever detection system you choose, you must ensure it complies with the relevant hygiene standard you set for your business. It must be specific to the food or beverage being inspected and suit your cleaning and maintenance methods.

What if products are in metal packaging?

The packaging material of a product can impact detection levels to a differing degree, depending on the inspection technology used. Both metal detection and x-ray inspection technologies are commonly used to inspect a wide range of packaging types/materials that are frequently used in the food and pharmaceutical industries, such as:

  • Plastic trays or overwrap
  • Paper
  • Metallised film
  • Aluminium foil
  • Glass
  • Metal cans
  • Ceramic pots
  • Doypacks (stand-up pouches)
  • Composite cartons/ tubes.

Foil-packed products, or those in any other type of metallic packaging, present the greatest challenge.

The gold standard in these circumstances is to install an x-ray detection system. X-ray systems need to be compliant with BRC, supermarket codes of practice and feature an advanced linear array with proven inspection algorithms.

The main thing to remember is that metal-based packaging provides a barrier to more traditional metal detectors. So, if your product packaging involves any metallic materials, an x-ray inspection system should be the preferred choice for your processing line.

For complex packaging types such as cans and glass jars, special contamination tools are available to detect contaminants on the edges of the packaging. Complex software algorithms are used to inspect the packs, and the x-ray scanner can be instructed to inspect only detailed areas of the packs.

Where in the production line should I place my metal detector?

To identify metal contaminants in food processing, metal detection systems – both metal detectors and X-ray machines – can be placed throughout the food production process. The only exception is with packaged products. With these, a food metal detection system can be placed at the end of the production line, as a final product check before sending it out.

Manufacturers need to identify their CCPs as part of their HACCP as this will help in the choice of optimum location/s for the placement of metal detection systems or x-ray machines. Establishing CCPs is an essential step to ensure the highest standards of food safety. A CCP is the point at which control must be applied to reduce the risk of contamination to safe levels.

X-ray inspection systems, being the more advanced technology, can provide an appropriate detection solution for each CCP.

A CCP may occur at the point raw materials enter the process, or when ingredients go through a sieve, come into contact with mixing blades, or during the rolling process or the final cutting-back stage. Essentially, at any stage where a change happens, or where ingredients come into contact with potentially damaged metal machinery.

The CCPs will be unique to each manufacturer, but it is vital that at each stage where a contaminant may enter the process, a metal detection machine must be installed.

How to avoid false readings

False readings can be costly in terms of product wastage and downtime, so it’s essential to do what you can to avoid them. Here are five factors to consider:

  1. External, environmental factors

Metal detection systems, by their very nature, are sensitive pieces of machinery. Try to place them away from areas of high vibration, areas particularly susceptible to temperature changes and where air-borne electrical interference could affect their readings.

Before deciding which detector is best for your operating environment, it is vital to assess your food production areas.

  • Do they provide a dry or a wet environment – or possibly both – that could arise in a product effect?
  • Are there any variations in temperature?
  • Ensure, if possible, that your systems are positioned away from areas of high vibration.
  • Things like cables, inverters and variable-speed drives may cause electromagnetic interference, which will likely cause erratic operation and false rejections. 
  1. Product characteristics

The product effect is a significant factor when it comes to causing false rejections. It is caused by certain features of the product (such as high salt or moisture), which can disturb the voltage balance received by the coils.

  •   Does the product have high salt and/or iron content? If you are producing snacks, such as crisps and nuts, bear in mind that these types of product generally contain a high dose of sodium, making them highly conductive. This can cause metal detection systems to trigger false results and raise your wastage figures.
  •   Does the product have high moisture content? Many products have a high water or moisture content. These include fresh meat and fish and cheese. With these types of products, you need to set your detector so that the product effect is eliminated.
  •   Are there variations in the product’s temperature? As warm products cool down and frozen products begin to thaw along the line, these changes can affect the product’s signal.
  •   Is the product packaged in a metal film? As discussed before, in this scenario x-ray detectors are most likely your only option.

If the answer to one or more of the above questions is “yes”, you need to select a metal detection system with the correct frequency, to avoid any product effect.

A smart option is to choose a multi-head metal detector. These are more effective at handling a variety of signal variations.

  1. Product uniformity

Here, you need to consider the range of products to be checked and to consider if they change consistency as they go through the production process – or due to changing environmental factors. If their salt or moisture content varies, as it will if the temperature and humidity in the plant changes, then this will have an impact on the effectiveness of the metal detector: this is because frequencies pass through products in a different way depending on the product make-up. 

  1. Advanced technology

The introduction of checkweigher combination systems is a big step forward in cases where space is at a premium and will reduce the total cost of the solution. A metal detection search head takes up less space than an x-ray inspection unit, so in situations where installation space is limited and metal is the likely contaminant, a metal detector may be the best solution.

Checkweigher combination systems are ideal for manufacturers supplying a variety of products to the big supermarkets, as they ensure compliance with the grocers’ codes of practice and regulatory stipulations.

  1. Work with the experts

When making such a significant investment, it is vital to get it right. We cannot stress enough that getting expert advice is essential. Experts in this field will help analyse your working environment, the types of product you need tested and will then be able to advise you which testing equipment will work best for you. Consider trialling the equipment as part of this process or visiting reference sites. 

How to maintain metal detection systems

It’s important to ensure that the equipment is correctly maintained throughout its service life, so that it can operate at optimum performance with maximum uptime. An equipment maintenance programme ensures that future mechanical or electrical problems can be addressed before a breakdown occurs.

Once you have carried out a detailed analysis of your product, the food processing environment and consulted with experts, you will be able to make the best choice for your food processing and packaging lines.

Both metal detection and x-ray inspection systems also require regular performance monitoring checks to be carried out at prescribed intervals.

To keep your choice of metal detection system running at optimum performance levels, you must ensure that it is installed properly, to the highest of standards, and that it is regularly maintained. Not only must you follow the manufacturer’s cleaning instructions, but you should also carry out regular maintenance checks – and keep a store of spare parts.

By doing this, you will reduce the likelihood of false triggering and extend the life of your metal detection equipment.

Reducing waste and improving efficiencies

Metal detectors have become highly complex pieces of machinery. They are equipped with web-based software which means data can be collected from multiple sites, processed and linked to an SQL-database. SQL, or Structured Query Language, is the standard means of manipulating and querying data in relational databases. It provides real-time analysis so that live line status can be viewed on multiple PCs within corporate networks.

Some of the best metal detection systems available on the market can be remote controlled, with information uploaded and managed from a central database. This means it is easier and faster to identify rejected items and quality control data. What’s more, by uploading all data to a central database means all events are stored and archived for compliance purposes and audits.

Summary

Here’s a checklist of what a state-of-the-art metal detection system should have. We hope this will help you make the correct decision when investing in a metal detection system for your production lines. It applies across a wide range of industries from frozen or fresh produce, animal feed, pharmaceutical, snacks, ready meals or chemicals, and many more.

  • Instant real-time data collection
  • Capability to analyse data by line, product, shift and site
  • Suite of analytical tools for informative reporting
  • Capability to produce audit records from a wide range of production equipment
  • Easy to operate with minimal training
  • Accurate production monitoring and compliance to customers’ specifications
  • Instant email alerts for non-compliance incidents
  • Provide product performance reports to help improve productivity and push down the cost of waste
  • OEE, or Operating Equipment Efficiency

We cannot stress enough the importance of data monitoring and the ability to measure statistics. Being able to do this will greatly increase productivity, reduce downtime and identify areas for improvement. And it will not be long before this translates into higher sales volumes and profits.

Contact us today to find out more about metal detection

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