Foreign material contamination is a serious risk. Contaminants in products can trigger consumer complaints, harm your brand’s reputation, and at worst, be a choking hazard or cause injury to the teeth or digestive tract.

While preventive measures like equipment maintenance, sanitation, and supplier controls help, foreign materials can still enter production. That is where detection technology becomes essential.

This article provides an overview of common contaminants, how metal detectors and X-ray systems—the two most important foreign material detection technologies—work, their strengths and challenges, plus the current trends and outlook of contaminant detection.

Common Types of Foreign Contaminants 

Foreign materials fall into two categories: metallic and non-metallic.

Metallic contaminants are the most common. These include metal shavings, equipment parts like screws, bolts, or wire fragments, and even personal items like hairpins. It is important to detect and prevent contamination with metal objects because not only are they a hazard for consumers, they can also damage equipment, causing lengthy downtime.

Non-metallic contaminants are also a growing concern. Bone fragments, rubber from equipment and utensils, glass from packaging, and wood fragments can all enter the production stream. These are not findable by metal detectors, and some can even be challenging to detect with food X-ray equipment. 

How Metal Detectors Work

Food-grade metal detectors use a magnetic field to detect metal within a product. When a metal object passes through, it disrupts the field. Receiver coils detect the signal change, and the system flags or rejects contaminated products.

Detection effectiveness is influenced mainly by the type of metal:

• Ferrous metals (iron, steel) are easier to detect due to high magnetic and conductive properties.
• Non-ferrous metals are detectable based on conductivity. High-conductivity metals like silver or aluminum are easier to detect than low-conductivity stainless steel.

To detect both types of metals, dual-frequency metal detectors use two bands simultaneously: lower frequencies for ferrous and higher frequencies for non-ferrous metals.

Other factors that can affect metal detector performance:

• Contaminant orientation: The signal level generated by a contaminant is proportional to its surface area as it enters the field. A small piece of metal standing upright may trigger a stronger signal than when lying flat.
• Product properties: Temperature, salt, or iron in the product can cause false positives.
• Tunnel aperture: Smaller apertures generally improve detection, though oversized apertures may be needed for highly reactive products.

Metal detectors effectively protect applications from metal contaminants. Exceptions are stainless steel and products in metalized film or foil packaging.

How X-Ray Systems Work

X-ray inspection systems generate a beam that passes through the product. A sensor on the other side captures the energy that remains after passing through the product and creates a grayscale image based on density differences.

Since most contaminants (e.g., metal, glass, bone) are denser than food, they absorb more energy and therefore they show up as dark spots in the image. X-rays are especially effective for detecting high-density contaminants and are not affected by temperature or packaging material.

Detection sensitivity depends on:

• Contaminant density and thickness
• Product thickness
• Size and contrast between product and foreign object.

X-ray systems can detect ferrous, non-ferrous, and stainless-steel metals, plus mid-density materials like stones and bones, as well as contaminants in foil packaging. Detection becomes more challenging with low-density materials, especially those that have the same density as the surrounding product. 

Why Add Contaminant Detection to Production Lines?

• Reduce risk: Metal detectors and X-rays support HACCP plans and reduce the risk of costly recalls, legal action, and brand damage.
• Regulatory compliance: Even small fragments may require a product recall under USDA and FDA regulations.
• Quality assurance: Detection systems can help validate your safety programs and reduce product loss and downtime.

Five Steps to Choosing the Right Detection Solution 

1. Identify target contaminants: Conduct a risk assessment to understand which foreign materials are most likely.
2. Assess product properties: Consider the size, shape, density, line speed, temperature, and packaging of the product.
3. Select technology: Where possible, use both metal detectors and X-ray systems. Each has strengths depending on the contaminant and application.
4. Determine placement: Common detection points include post-grind, post-deboning, after primary or secondary packaging.
5. Add rejection system: This removes faulty products from your line.

The Future of Contaminant Detection

Though the basic principles of metal detectors and X-rays date back decades, newer algorithms and hardware continue to improve sensitivity and accuracy.

One major advancement is dual-energy X-ray systems, which use two energy levels to detect a broader range of materials, like bone and rubber.

Two key trends are shaping the future:

• Automation: As lines become more automated, the potential for machine-related contamination rises while human oversight decreases. Detection is important to keep risk under control
• Globalization: With international supply chains, global brands are standardizing contaminant detection strategies across all locations.

Emerging Technologies

In addition to traditional detection systems, newer options are gaining ground:

1. Hyperspectral imaging: Identifies contaminants based on light absorption and reflection 
2. Vision systems: Use cameras and software to detect surface defects or contaminants
3. Near-infrared (NIR): Distinguishes organic from inorganic materials by using NIR light
4. Ultrasonic detection: Uses sound waves to detect foreign objects.
5. Thermal imaging: Detects foreign materials based on their thermal properties.

Whether dealing with metal fragments or more complex threats like bone or rubber, the right detection technology helps today’s manufacturers protect their customers, their brand, and the bottom line.