KANSAS CITY, MO -- Metal detectors and other inspection and detection systems play a critical role in helping dairy processors prevent recalls tied to foreign materials.

The contamination of milk and dairy products can affect quality and food safety for human consumption. Given that metal is everywhere in the food supply chain, automated equipment is now often deployed in dairy processing plants to improve efficiencies and product costs. Within factories are a wide array of mixers, dicers, slicers and pumps, most of which are made from stainless steel.

Most dairy products are challenging for metal detection inspection since they exhibit a phenomenon known as ‘product effect’. This is where the type of product being inspected can itself hinder the inspection technologies capability to identify a particular contaminant.

Many dairy products naturally exhibit high ‘product effect’ due to high moisture content, generally referred to as ‘wet products.’ The high moisture content in dairy products makes them relatively good conductors and thus more likely to produce a signal in the metal detector in the same way as small metal contaminants would. This product effect makes it more difficult for the detector to distinguish between the product and the metal contaminant.

It is important to have a metal detector at each stage on the line, said Camilo Sanchez, metal detection product line manager at Columbus, Ohio-based Mettler Toledo. Having a pipeline detector for pumped products prior to packaging can remove any metal before further value is added to the product, reducing waste and keeping profits as high as possible. 

“Pipeline applications are wide and varied, choosing the right metal detection solution will ensure maximum performance and brand protection,” Sanchez said. “A variety of integrated reject devices are available to efficiently remove metal contaminated product from the production flow while minimizing waste of good product.”

Having multiple metal detectors on various lines is important in allowing dairy processors to check for metal contaminants throughout processing, a setup that also makes it easier for dairy processors to pinpoint the source of contamination. When it comes to pumped products such as milk and yogurt, shards from stainless-steel equipment upstream are a potential issue because the metal is so widely used in dairy processing operations. Piped metal detectors and X-ray inspection systems can identify and reject such contaminants before further processing. But small stainless steel and other metal contaminants still can present a challenge for metal detectors.

For Advanced Detection Systems, Milwaukee, simultaneous, multiple frequency metal detector technology is available and being further developed to reduce the effects of conductive products that are difficult to accommodate while achieving best possible detection levels. 

“Magnetic separators are best used upstream of the metal detection system,” said David Smith, sales manager for ADS. “Magnets quietly remove ferrous contamination without disrupting production. Metal detectors and their integrated reject devices are best used to detect ferrous, non-ferrous and stainless-steel metal missed by the magnet.”

Magnetic separation and filters are an effective means of removing contaminants from pipe-fed liquids. Pipeline metal detection systems equipped with fast-acting divert valves are space-efficient, economical systems for detecting and removing metal contaminated product. Metal contamination risk downstream of the pipeline metal detection system during filling and sealing of viscous product can be mitigated by using X-ray equipment which can also accommodate metalized film often used to seal packages, Smith said.


With regard to metal detection, the best possible detection levels are an ever-present challenge. Dairy processors can help themselves by using metal detection following the point where there is no further risk of contamination and at a point in the process where the smallest possible metal detector aperture can be used, Smith said. Also, attention paid to presenting the product in a consistent way when it comes to weight, volume, temperature and orientation allows for best possible metal detection levels.

Metal detectors are not an effective method of detecting metal contaminants in packages that have a metalized film seal or other metal components.  The metal detector cannot be adjusted to ignore the package’s metal component while detecting metal contamination in the product, said Smith.

Steve Mason, national sales manager at Fortress Technology, Inc., Toronto, agreed. Previously, dairy processors might have installed magnetic separators at the first phase of processing to remove ferrous metals, he said. However, today’s metal detectors are so advanced they tend to be more effective at eliminating metal foreign contaminants in all types of dairy products.

Metal could also be introduced upstream, he said. For example, a can of soda discarded in a field of grain, which is then harvested using powerful tractors, means that metal fragments, many of which are non-magnetic, can easily be dispersed. For dairy alternative products like oat or almond milk, incidents like this could be brand-damaging, as well as a health risk to consumers. If a metal contaminant is caught in its largest form at the start of the processing line, it is eliminated at the cheapest part of the process.

Previously, a team of manual operators would visually inspect wear of machine parts and wire mesh from sieves, Mason said. However, with fewer manual workers on processing lines, the risk of metal contaminants increases.

Fortress advises processors to always consider the whole contaminant picture – pest control, good manufacturing practice, machine maintenance, design of the production facility – as well as workforce knowledge. Although foreign material control is inherently process-driven, if people aren’t trained to understand what could go wrong and what to look for, product integrity can still be compromised.

“There are virtually no limitations to installing metal detectors,” Mason said. “Although specific features of likely contaminants, the product, packaging, processing and supply chain may determine whether metal detection is chosen for a particular point in the process. If a dairy processor needs to detect other physical contaminants, for example, glass or bone, they may opt for X-ray. However, this technology might not be viable for specific applications.”

From research Fortress has conducted with food manufacturers and dairy processors over the years, naturally occurring food contaminants such as fruit pits or shell remain the most prevalent consumer complaint. Closely followed by insects. However, contaminants that could potentially harm a person – such as glass, rock or metal – are still the most potentially brand-damaging.

Foil is also a primary contaminant on dairy processing lines due to the widespread use of items such as masks, hair nets and gloves. They are often designed with a foil strip in them, making items visible to a metal detector.

Hygiene can be another challenge. Adhering to best practice is critical. While standards are typically high in dairy plants, the COVID-19 pandemic has certainly reaffirmed the importance of conveying confidence to consumers, Mason said. 


Fortunately for dairy processors, suppliers of metal detectors continue to introduce advances that improve the process.

Mettler Toledo offers metal detectors for all types of dairy products, including pumped slurries, unwrapped cheese, and packaged products. Their Profile Advantage metal detector is designed for pumped and conveyorized products. Due to the high moisture and saline content, dairy products can exhibit product effect, where the product itself interferes with the sensitivity. The Profile Advantage metal detector, which uses multi-simultaneous frequencies to overcome the product effect. The Profile Advantage metal detectors use various combinations of high and low frequencies simultaneously, along with built-in Product Signal Suppression technology with two stages of discrimination, frequency and phase. This cancels the information from these combinations of high and low frequencies to effectively remove the product signal or ‘Product Effect’, allowing for much smaller metal contaminants to be detected.

Other technological advances include metal detectors that have automatic Condition Monitoring which continuously monitors the functionality to assess key component performance and to give advanced warning of adverse trends that could lead to equipment failure if left unaddressed. Early warnings can be communicated via SMS text messages or email to key operational personnel.

Recent software developments from Advanced Detection Systems allow dairy processors to make better use of their metal detection investment. The web server-enabled touch screens have simplified the task of documenting metal detector events and identifying authorized changes of metal detector settings. These operating features make it easier to document proper usage of the metal detectors in service and maximize the dairy processors investment in the metal detection equipment. 

Simultaneous frequency is the most reliable way to remove product effect without compromising the sensitivity of a metal detector. Fortress uses ARM microprocessors to adapt to these changing product characteristics. This processing technology powers the Fortress Interceptor, enabling it to run real-time analysis of the low-frequency and high-frequency signals in parallel. The Interceptor can also be utilized to detect metal contaminants in free-flowing pumped dairy liquid or powdered product. Other valuable benefits include the ability to more accurately inspect product packaged in metalized film. AutoPhase is another useful tool that can help to counteract product effect.

As food processing plants get smarter, technology becomes even more imperative. Integration, productivity and digitization are the main trends processors and suppliers are observing.

“Driven by ever-stricter safety regulations and the need for traceability across the supply chain, many are turning to inspection solutions with improved precision and greater digital capabilities,” said Mason. “Smarter technology is being used within or alongside inspection systems to improve efficiency, compliance and, ultimately, profitability.”

This story is featured in the June 2021 issue of Dairy Processing.