In the dairy industry, ensuring the safety and quality of products is paramount, making metal detection an essential component of operational processes.

Processors and their supplier partners work continuously to avoid contamination of milk and other dairy products, which can affect quality and safety of the product, and protect food for human consumption.

Product effect

Conductivity referred to as “product effect” is a key factor to be considered when determining how metal detection will be used in a specific application.

“In the dairy trade, product containing salt, fat and/or oil can be quite conductive compared to dry products,” said Robert Slauson, assistant sales manager for Milwaukee-based Advanced Detection Systems. “Metal detectors perform better and are easier to use in less conductive products; so with conductive dairy applications, it’s important for processors to understand the conductivity of their product and factors that impact product effect and detection levels.”

These factors include the temperature, orientation and volume of product being presented to the detector at a given time. To the extent that these factors can be controlled, processors should do so in an effort to minimize the impact of product effect on their detection levels.

“Product testing up front and use of the metal detector’s own software features are effective ways to measure product effect in a particular application,” Slauson said. “After doing so, metal detection will be enhanced if steps are taken to ensure that the temperature, orientation and mass of conductive product presented to the detector is consistent. If product effect is not kept consistent, detection levels might be sacrificed in order to accommodate the lack of consistent product effect.”

Mettler-Toledo Product Inspection offers technologies for piped applications such as milk, yogurt and ice cream, and for bulk products such as cheese and packaged. It also offers different types of detection systems designed for highly conductive products where product effect is likely (such as cheese), as well as one-pass automatic setup and a clustering capability for easy product changeovers.

“Metal is common and can come from incoming ingredients such as milk powders, or be introduced into liquids/slurries after mixing [if small chards break off from equipment and enter the production line],” said Sarrina Crowley, marketing communications manager for the Lutz, Fla.-based company. “We offer metal detectors that can be placed in critical control points, such as gravity flow units at the beginning of the line to avoid adding further value to the product and wasting profits, as well as piped metal detectors and conveyorized for end of line inspection.”

Establishing requirements

Dairy processors should establish clear requirements and expectations when selecting detection systems.

Bunting Magnetics provides metal detection solutions designed for a range of dairy applications, including liquids, powders and solid products. The company said its solutions help prevent metal contamination at various stages, from raw ingredients to final product inspection. It also has X-ray systems that offer broader detection capabilities, identifying contaminants such as glass, stone and dense plastics, in addition to metal, making them ideal for comprehensive food safety assurance.

“Our primary focus is detecting metal contaminants, particularly stainless steel, which is prevalent in dairy processing due to the nature of the equipment used,” said Jim Thiessen, North America trade show manager for the Newton, Kan.-based company. “Identifying stainless steel can be challenging because of product signal interference. Our advanced technologies, including Triple Frequency detection, enhance sensitivity and adaptability, improving accuracy even in complex product environments.”

Fortress Technology offers a wide range of inspection applications targeted at the dairy processing sector, ranging from pipeline metal detectors for pumped products, to inline metal detectors, X-ray systems and combination machines.

Matthew Gidman, product manager at the Toronto-based company, noted processors most commonly will choose end-of-line contaminant inspection technology when products are packaged, especially for applications such as sliced, grated or packaged cheese, yogurts, and other dairy desserts.

“Specific features of likely contaminants, the product, packaging, processing and supply chain will usually determine whether metal detection or X-ray is chosen for a particular point in the process,” he said. “Having several units spread throughout the line can also help to identify much faster where the source of a potential contaminant might be.”

To help address higher costs, many dairy processors inspect liquids by using pipeline systems. Upstream is often the place where processors can get two or three times the performance level.

“If a dairy processor needs to detect other physical contaminants, for example glass or plastic, they may opt for X-ray,” Gidman said. “It is important to note that X-ray systems are more likely to be affected by other parameters such as the shape of product and the mode of transport through the unit, in addition to density differentials.”

When both technologies are used on a production line, X-ray machines are typically most effective for end-of-line inspection, providing a final check before products leave the facility. Metal detectors, however, continue to offer greater versatility, fitting seamlessly into multiple stages throughout the process.

“Metal detection can also be better suited for tighter spaces, can handle higher speeds and extreme temperatures, and require less maintenance compared to X-ray systems,” Gidman said. “This makes metal detectors an excellent choice for both end-of-line checks and critical control points earlier in the production flow.”

Efficient tech

Processors should have a site study conducted to determine what the potential hazards are and the best technologies to prevent problems.

Automated equipment is now often deployed in dairy processing plants to improve efficiencies. Plants also contain a wide array of mixers, dicers, slicers and pumps, most made from stainless steel.

“The sensitivity of metal detectors plays an essential role in accuracy,” Gidman said. “Reducing the aperture size in relation to the product size can be a simple and effective way to increase metal detector sensitivity and address issues like orientation effect. This is because sensitivity is expressed as the smallest detectable spherical contaminant travelling through the geometric center of the aperture.”

Additionally, dairy product applications are typically wet and conductive, which can present another challenge for metal detectors. Cheese, for example, with its high moisture content, combined with salt, can be highly conductive and cause a reaction like metal being present.

“Using simultaneous multi-frequency technology is the most reliable way to remove product effect without compromising the sensitivity of a metal detector,” Gidman said.

Slauson noted conveyor mount systems are ideal for sealed packaged product ensuring that metal contaminants will not be introduced into the product following metal detection. 

“Pipeline systems are ideal for upstream metal detection of product, (i.e. ice cream) prior to packaging,” he said. “Detection levels are enhanced due to the typically small diameter of the detector. Metal is detected earlier in the process, avoiding adding value to contaminated product and rejection of contaminated product is efficient with the use of a three-way sanitary valve operating as an integral component of the metal detection system.”

Ensuring protection

The number one requirement for all food manufacturers is to ensure products are safe for consumption. Inspecting products after packaging using an end-of-line metal detection and/or X-ray system is the most important CCP. For most retailers, it is also a contractual requirement.

“Advanced Detection encourages use of our free product testing service to ensure that our metal detector is designed and built for best possible detection levels in our customer’s specific application,” Slauson said. “Once installed and in service, our customers regularly challenge the detector each day with certified test wands to confirm that the metal particles are detected and rejected as required.”

Mettler-Toledo and others offer nationwide field service, 24/7 telephone support, and ProdX data management software to enable ease of record keeping for audits.

Whenever there is a change in a process or packaging, Gidman recommended QA or risk professionals revisiting inspection protocols and hypothetical contamination scenarios.

“Even when there is no significant change, food processing inspection risks should be reviewed annually as part of a defined HACCP assessment,” he said. “The other important feature to consider is documentation and reporting. For traceability and audit purposes, records must be retained to verify that each system is performing to defined FDA and GFSI food safety standards, and to prove that inspection procedures are being followed consistently and correctly.”

Regular calibration and maintenance are critical to keeping detection systems in peak condition, according to Thiessen.

“We recommend that all inspection equipment undergo evaluation and testing by a factory-trained technician at least once a year to maintain optimal performance and compliance with safety standards.”