Part 1: Basics of Metal Detection in the Food Industry

Why are metal detectors used in the food industry?

Metal detectors for food primarily are used for the purpose of consumer protection. Despite maximum care metallic contaminations of food products during the production process cannot be fully excluded. Metal particles that enter the product during the production process or already are contained in the raw material may cause serious injuries of consumers. The consequences for the producing company are numerous and serious and include compensation claims and expensive recalls. Even bigger and longer-lasting damage is caused by the negative brand image and the loss of consumer trust caused by impure food products.

Metal detectors for food provide effective protection against ferrous and non-ferrous metals (aluminium, stainless steel, etc.). They can be installed in every step of the production process and can be used for many different applications, e.g. for the inspection of bread and bakery products, meat and sausage product, fruit, vegetables, dairy products, spices, sugar, etc.

In addition to consumer protection, metal detectors also are used to protect machinery. Even smallest metal particles can lead to machinery failure. Expensive repairs and production downtimes are the consequences, often followed by revenue decreases.

Where are metal detectors installed in the food production process?

When used for machinery protection, the metal detector is installed directly before the machine to be protected. If, as in most cases in the food industry, consumer protection is the goal, several inspection points are useful. An inspection of raw material has the advantage that metal particles are separated before they are broken up into smaller pieces which might be harder to detect. Inspections at critical control points (HACCPs) during the production process are recommended to notice machinery failures (such as broken blades) in time.

Consequently, food products in their final stage after packaging are inspected once again with a metal detector (or an X-ray system) to fully exclude contamination.

For optimal product protection an inspection of raw materials, of several critical control points, and a final inspection of the finished product are recommended.

How do metal detectors work?

Basically there are several types of metal detectors that operate with different detection methods. In the food industry, metal detectors usually apply the transmitter-receiver method (see graphic).

Such metal detectors are equipped with a transmitter coil and two receiver coils. The transmitter coil generates a constant electromagnetic field. When a metal particle passes the detector it interferes with the electromagnetic field, causing a signal to be detected by the receiver coils. The electronic unit in the metal detector analyses this signal, evaluates it and signals a metal contamination. As a rule metal detectors in the  food industry are equipped with automatic reject units that directly separate the contaminated product from the production line. 

Here you can find all parts of our guidelines on contaminant detection in the food industry

Part 1: Basics of Metal Detection in the Food Industry
Part 2: Use of X-ray Inspection Systems in the Food Industry
Part 3: Determining Critical Control Points in Food Production Processes
Part 4: Testing of Contaminant Detector Performance According to BRC Standards