Metal Contamination in Food Industry- Detection & Reduction

Metal Contamination is type of contamination where product is contaminated with metal particles that comes in contact with manufacturing  product and is a primary concern of consumer safety and product quality. Occurrence of  contamination in food can be by various ways and is considered as a big headache in industries such as food, beverage, pharma, chemicals and packaging industries.

  1. Sources of Metal Contamination in Food

Contaminated raw material, not following Good Manufacturing Practices inside processing hall, poor installation and lack of maintenance can be major source of metallic contamination. In food industry most common type of metallic contamination are categorized into three category.

Some of the major source of metal contamination in food industry are shown in the below diagram.

  1. Preventing Metal Contamination

To develop any preventive measure it is essential to have full understating of all possible way of metal contamination can occur in food product. Most effective method of preventing metallic contamination is having a fully developed and efficient metal detection system

2.1. Primary screening of Ingredient

Processing ingredients should be inspected and checked for metallic contamination if any, as there is chances or metal being disintegrated into fragments during processing and hard to detect in later processing steps. Following points to be confirmed before accepting raw material-

  • Raw material containers to be staple free as there are chances of staple pins to fall in product during de-bagging the product.
  • Avoid using meat and carcass with metal tag on them as they are sources of metallic contamination.
  • Passing all incoming ingredients through metal detector or magnet traps for early detection and prevention.

2.2. Preventive Maintenance Plan 

  • Identification of any defective or faulty equipment to be shared and required steps for maintenance to be take care immediately.
  • Maintenance should be carried out in a planned way, aiming for minimum rear and tear.
  • Critical location, prone to metallic contamination to be specified
  • Keeping record of maintenance and corrective action carried out
  • Maintenance and checked details to be indicated on equipment itself for information purpose.

2.3. Following Good Engineering Practices

  • Maintenance inside processing area can led to remaining of metallic components in processing line or any adjacent area, hence all maintenance work should be done outside the processing building where ever possible.
  • After maintenance, equipment should be thoroughly cleaned before re-installation.
  • All maintenance tools should be codes or marked when being taken into processing section.

2.4. Following Good Manufacturing Practices

Operators or workers being exposed to food product or entering food facility should avoid carrying items such as watch, paper clips, staples, finger ring, earrings, pin, non-metallic pen, neck piece, bracelet, or any metallic item that is forbidden in the processing facility. 

 Metal Detection System

3.1. Introduction

A way forward to fight this serious condition is developing an effective metal detection system in food industries. Following evident advantages can be easily achieved by incorporating a metal detection system in existing food safety system of manufacturing units:

  1. Metal free high quality and safe product increasing brand trust and retailers confidence.
  2. Compliance of all regulatory and legislative requirement in reference to industry standards.
  3. No product failure hence low probability of product recall.
  4. Identification of superior quality raw material suppliers.

These points helps manufacturer in achieving better brand value along with reduced overall operating cost. 

3.2. Components – Metal Detecting System

Metal detector consist of following principle parts

  1. Detector Coil- Product passes through aperture, an opening, and detector coils in them are responsible for the detection of metallic contaminants. There are many technologies out in market involved; however, there are majorly two main categories of detector coils.
  2. Search Head Type detector coil– Able to detect metal contaminants of ferrous, non-ferrous and SS nature in foods that are packed or unpacked in metalized films.
  3. Foil in Foil Type detector Coil- Able to detect metal contaminants of ferrous and SS nature in foods that are packed in Aluminum foils.
  4. User Interface- It is a control panel that helps operator set various parameter and to check during processing for any required changes.
  5. Transport System- In most cases it is a conveyor or pipe chute, which helps in the forward movement of product through aperture.
  6. Automatic Rejection System- System for rejection of detected contaminated product from the uncontaminated product. Mostly fitted to transport system they are of various kind like air blast, push arm etc. and are selected on basis of product, process requirement, etc.
  7. Accessories
  8. Collection Bin- Lockable container for holding rejected product and is equipped with alarm to let know the bin is full.
  9. Covering Lid- Cover both detector and rejection device in full length
  10. Alarm System- Safety Alarm for faulty metal detector
  11. Reject confirmation devise- Senses the rejected item and time of rejection for future reference of validation & verification. 

3.3. Metal detector

Metal detectors are equipment that are now being widely used in food & pharma industry for safe and superior quality item production. Metal detectors are one of the important front line metal detection system and advisable to used and even considered as CCP before finished good dispatch.  

Metal detector comprises of coils (Multiple coils for more effective magnetic field)  connected to high frequency radio transmitter and when a metal passes through the first coils this high frequency field is disturbed. This disturbance causes changes in the voltage that is interpreted as output.

Metal detectors can be used at various stages of production-

  1. After processing line- Detection of any metal residue from maintenance, broken metal particle from processing equipment and human errors. Before filling & Packing line, metal detector can prevent the dispatch of faulty final product.
  2. Before processing line- For raw material inspection at material reception. This helps as primary screening and rejection of metal contaminants by initial screening preventing usage of contaminated material for processing.
  3. In-processing- Integrating metal detectors in process CCP can be used for detection of any chances of malfunctioning of equipment such as breaking of blade or any part into the product or that can result in the failure of processing equipment that can result in high cost maintenance.

3.4. Sensitivity

Actual operating sensitivity gets fluctuates and factors affecting loss in sensitivity are

3.4.1. Metal Type-

Metal contaminants found widely in food industry can be categorized in

  1. Ferrous– Easily detected as it is both magnetic and conductive
  2. Non- Ferrous– Doesn’t possess magnetic nature but is good conductor
  3. Stainless Steel – Most difficult to detect, as its poor conductor as well as shows non-magnetic feature.

The below table can be considered for general acceptable limit in both dry and liquid product.

Aperture Height

Dry Product

Wet Product

Wet Product


Ferrous & Non- Ferrous


Non- Ferrous

Up to 50mm




Up to 125mm




Up to 200mm




3.4.2. Orientation and shape of metal

Orientation affect is of great importance as orientation of metal passing in particular direction can be easily detected than another position, when the size of contaminant is lesser than the set required sensitivity.

  1. Ferrous contamination– Easy to detect if in parallel to direction of movement while difficult if in right angle to moving direction.
  2. Non Ferrous contamination– Easy to detect if in right angle to direction of movement while difficult if in parallel orientation.

3.4.3. Aperture Size-

Sensitivity of smaller opening or aperture is more than large opening.

3.4.4. Product Characteristics-

Dry products with contaminants can be easily detected when passed through detector compared to wet product due to the product effect signal generated from product influences the sensitivity of the detector, which can be maintained by using low frequency range of detection.

Metal detectors for food provide effective protection against metals contamination and can be installed in every step of the production process of various product such as for the inspection of bread and bakery products, meat and sausage product, fruit, vegetables, dairy products, spices, sugar, etc. Today, the food industry produces goods with the utmost efficiency, creating as much quality products as possible and also the detection technology meets HACCP requirements.


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