Pros and cons of metal detectors for fresh produce inspection

metal detectors for fresh produce inspection

Thinking about investing in a metal detector to inspect your fresh produce?

Over the past few years, Australia’s major supermarkets – Coles, Woolworths and Aldi – have been pushing Australia’s fresh produce suppliers to implement metal detection systems. 

But it was only after the strawberry crisis hit in 2018 that many producers have started thinking seriously about the investment. One major strawberry supplier in WA started scanning for metal contaminants in the middle of the crisis in a smart move to save the state’s industry. (Here’s what Australian food processors can learn from the strawberry crisis.)

The question is how do you know if a metal detector is the right inspection solution for your line? How do you make sure you’re getting the best ROI? Will metal detection tick all the compliance boxes for your customers? And can you ever really guarantee that your fresh produce isn’t contaminated?

In this article, we’ll outline the pros and cons of metal detectors so you can make an informed decision. 

But first, a quick recap on how metal detectors work

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Metal detectors can find small particles of ferrous, non-ferrous and stainless steel in products. 

They work by using coils wound on a non-metallic frame, which is connected to a high-frequency radio transmitter. When a metal particle passes through the coils, it interrupts the high frequency field under one coil. This changes the voltage by a few microvolts. The change might be minuscule, but it’s enough to tell the system that foreign material is present. 


Metal detectors can detect more than just metal

Traditionally, metal detection systems were only used to detect metal (including aluminium and wires), while X-ray inspectionsystems were used to detect all metals and other solid contaminants (glass, stones, bones, etc). 

But things have advanced and now, metal detection systems, such as Matthews’ systems by Bizerba, can detect non-ferrous metalstoo (these are metals such as aluminium that do not contain iron, are not magnetic, and are usually more resistant to corrosion than ferrous metals).

It can also detect non-metals such as glass and stones, as well as some other contaminants. 

New technology offers maximum sensitivity for contaminants

Newer advanced metal detection unitshave been designed to deliver maximum sensitivity for contaminants. And here’s the important part: they also maintain high resistance to interference. In the past, managing interference from other devices has been the biggest challenge with metal detectors. 

You can train the metal detector for specific products.

This means less manual adjustment is needed for different products. Changeovers become quick and easy, planned downtime is lower and productivity is higher. Check out the Bizerba VARICON+,which features a multi-product memory for up to 240 products.

Metal detectors can be installed almost anywhere along your line

Ideally, you should be putting your system at the stage in your processing line that has the most chance of finding contaminants. That’s where metal detectors offer an advantage:  they can be installed almost anywhere along the line. 

Because X-ray systems need a constant, known speed to construct images of the products they are inspecting, they don’t work in gravity-flow applications. However, metal detection systems can be easily adapted to suit your line, especially with most including variable speed settings. 

Though, as with X-ray systems, you will often get the best value by placing the system at the end of the line to examine packaged products. (If you are thinking about X-ray, here are 7 reasons why your business needs an X-ray inspection system.)

Metal detectors generally have a lower total cost of ownership (TCO)

When you weigh up the upfront cost against the total cost of ownership (TCO) over its lifetime, metal detection systems generally provide better value than X-ray systems. 

Here’s why:

  • X-ray systems are more expensive up front than metal detection systems
  • metal detectors last up to five times longer than X-ray

Learn more about how reducing TCO can help improve your bottom line.


metal detection solutions for fresh produce
New metal detection technology offers maximum sensitivity for contaminants, while maintaining high resistance to interference – previously always a metal detector’s biggest challenge.

Metal detectors offer less capabilities than X-rays

True, metal detectors can detect non-metals, but if you want to detect glass, stone or bone, X-rays are much more likely to suit your application. Two more things X-rays can do are check the shape and size of items, and count the number of items.

Metal detectors are sensitive to environmental factors

This is arguably the biggest drawback of metal detectors: they are sensitive to a number of environmental factors, such as 

  • temperature fluctuations
  • line vibrations
  • air-borne electrical interference

All of these things can make a difference to the inspection system’s performance. For example, freezing tunnels and hot water wash-down can result in false reject signals. Also, if you have other equipment nearby using similar technology, it may cause electromagnetic interference (EMI), resulting in erratic operation and false rejections.

This doesn’t mean you shouldn’t invest in a metal detector; it simply means you should select a metal detector that suits your inspection area. Ask yourself:

  • Is it wet or dry?
  • Is it high or low pressure wash-down?
  • Are there temperature variations?
  • What equipment is nearby? (so you can avoid sources of vibration and mechanical shock)
  • Are cables, inverters and variable-speed drives nearby? (to avoid EMI)

The “product effect” can cause false rejections by metal detectors

 What kind of produce are you inspecting? Certain product characteristics are able to disrupt the voltage balance between the receiver coils in a metal detector. So, the metal detector reacts as it would to a metal contaminant.

Characteristics that cause the product effect include:

  • high salt content
  • high iron content
  • high moisture content
  • variations in the product’s temperature, warm products cool and frozen products thaw along the line
  • metal film packaging (for obvious reasons) 

Again, this doesn’t mean you shouldn’t use a metal detector; you simply need to select the correct frequency to move the product-effect signal away from the signal of any contaminants. To do this, you need a multi-spectrum metal detector.

Metal detectors suffer from the orientation effect

Metal detectors are more sensitive to some metals when they are facing a one way, and less sensitive when those same metals are facing another way. For example, it’s possible to detect a pin in strawberries using metal detection so long as the pin is facing “the right way”. If not, your products could be a serious risk. (This piece on the top 10 considerations when assessing X-ray or metal detection for strawberrieswill help give an understanding.)

However, X-ray technology sees almost all metals as the same, regardless of orientation. 

If I invest in metal detection, is there a 100% guarantee that every metal contaminant will be found? 

Installing a metal detection system does not give you a 100% guarantee. But then, no inspection system will. Your goal is to considerably reduce the risk to consumers, which in turn reduces risk to your business. For this, you need to invest in the best-fit inspection system for your fresh produce and your production line. 

As we’ve shown in this article, the performance of your metal detector is impacted by its environment. Metal detectors for fresh produce inspectioncan be an excellent idea if you pay attention to proper installation and ongoing preventative maintenance to ensure you are getting a maximum ROI. 

That’s where Matthews Australasia can help. We have years of experience working with Australian fresh produce suppliers and food processors of all types and sizes. Tap into our expertise to select and install the right metal detection system for your line. We can also help train your staff in operating the system and provide a preventative maintenance program. (Here’s an interesting comparison between preventive maintenance versus breakdown repair.) 

Looking for more info about coding, labelling and vision inspection? Matthews’ large resource library is full of information for Australian manufacturers. Plus, it’s all free to download!

Back to reducing TCO: upgrading & using inspection equipment is one way to increase operational efficiency and eliminate waste This whitepaper explains how. Download Now

Image credits: iStock/ Peangdao (main); iStock/ Michele Jackson (middle)

Andrew Ball

Andrew Ball

Commercial Products & Marketing Manager at Matthews Australasia
Andrew Ball is an engineer and business professional with 25 years of broad industry experience. His career includes experience gained at Honeywell, Ford and Siemens, with over half of it invested in the coding and marking industry. At Matthews Australasia, Andrew and his team create and market innovative solutions, services and insights for Matthews’ customers and the broader industry alike. Aside from career and family, some of Andrew’s other passions include music, sport, fitness and reading.
Andrew Ball

by Andrew Ball

Andrew Ball is an engineer and business professional with 25 years of broad industry experience. His career includes experience gained at Honeywell, Ford and Siemens, with over half of it invested in the coding and marking industry. At Matthews Australasia, Andrew and his team create and market innovative solutions, services and insights for Matthews’ customers and the broader industry alike. Aside from career and family, some of Andrew’s other passions include music, sport, fitness and reading.

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