Sampling

Sampling is the selection of a small portion of product to exahstively test for quality and contaminents.  It is impossible to test everything to this level, so small portions (samples) are selected that are representitive of the whole production run.

Introduction

Sourced from the Canadian Food Inspection Agency at https://inspection.canada.ca/preventive-controls/sampling-procedures/eng/1518033335104/1528203403149, accessed on September 22, 2022.

X-ray Inspection Systems

Following Good Manufacturing Practices (GMPs) and a well developed Hazard Analysis Critical Control Point (HACCP) plan can help prevent, reduce or eliminate foreign contaminants in raw materials and finished products. Depending on your product and packaging, technology such as x-ray inspection systems can assist you as a tool within your foreign materials reduction program.

X-ray inspection systems are based on the density of the product and the contaminant. As an x-ray penetrates a food product, it loses some of its energy. A dense area, such as a contaminant, will reduce the energy even further. As the x-ray exits the product, it reaches a sensor. The sensor then converts the energy signal into an image of the interior of the food product. Foreign matter appears as a darker shade of grey and helps identify foreign contaminants.

Ideally, x-ray inspection should be done at several locations along the production line. Only inspecting at the beginning of the line means contaminants introduced at a later point on the line won’t be detected. The best location for x-ray inspection is at the end of your production line.

Benefits and uses

The benefit of x-ray inspection is the ability to identify possible foreign contaminants in your product. This reduces risk of customer complaints and possible recalls. X-ray inspection systems are known to detect:

• all types of metals
• calcified bones
• ceramic or concrete
• glass
• non-ferrous metals in foil
• PVC plastic
• rubber
• stainless steel
• stones
• teflon

The detection capability of contaminants is directly related to the density of the product and the contaminant. The denser the contaminant, the darker it will appear on the image and the easier it will be to identify. There are some contaminants an x-ray system may not detect, including:

• cardboard
• hair
• insects
• low density plastics
• low density stones
• paper
• soft bones (cartilage)
• wood
• thin glass (such as fluorescent tubes)

X-ray inspection systems are commonly used to monitor product quality. For example, they can be used to measure mass or density and can indicate that a package is under or overfilled. Other uses include monitoring for broken or damaged product, missing product components and head spacing in packaging.

Considerations when choosing an x-ray inspection system

1. Needs

Choose an x-ray model based on the size, weight and shape of the product, and the line speed. X-ray inspection systems have unique monitoring capabilities that metal detectors don’t have. Examples include:

• They reveal metal contaminants in food products that are packaged in metal containers, wrapped within a metal film or containers with metal lids.
• Food products with high salt and/or moisture content that normally reduce the sensitivity of a conventional metal detector can be monitored.
• Non-metallic dense contaminants, such as glass or stones, are detected.

2. Type of product

The success of x-ray inspection systems depends to some degree, on the food product. The thickness, homogeneity, density and size of the product determine the accuracy of detection for contaminants. X-ray inspection systems work better with homogenous products, like cheese, because they create clearer images of background interference. Non-homogenous products, like canned soup, will create uneven shades of grey and could give false readings, because soup can have different components with different densities.

X-ray inspection systems are not affected by product temperature. They are successfully used to inspect products at — 20 °C or + 90 ° C.

3. Automated versus manual inspection

The main difference between manual and automated systems is how the food items are handled and where the defect decision is made. In manual systems, the operator loads and unloads the food item from the machine and makes the defect decision based on the x-ray image. All manual systems include image enhancement hardware, which will electronically enhance the image. This is helpful because the defect decision is being made by the operator visually, so any tools to aid the human eye will reduce the chance of human error.

In automated systems, the food item may be automatically loaded by a conveyor or by an operator. Automated systems use software to make the defect decision and do not rely on the operator’s vision. The software compares the x-ray image with preset measurements and rejects defective products automatically. If a product is rejected, it can be removed with an automated rejection mechanism such as:

• air blow-off systems
• drop flaps
• retracting conveyors
• sweep arms

Magnetic Foreign Body Detection

Assessment and removal of metal contaminants is becoming common practice in the food processing industry. Many retailers make metal detection a critical control point (CCP) requirement in their supplier’s HACCP plans, to ensure finished products meet established specifications.

Metal pieces in food products pose a safety risk to consumers and can damage processing equipment. Sources of metal contamination include:

• incoming ingredients (contaminated during processing or transportation of the ingredient)
• processing equipment (grinding, crushing processes or general abrasion or vibration causing the loss of nuts and bolts etc.)
• inadequate personnel practices and environmental causes

Selecting a Magnet

Equipment that detects and removes metal contaminants is important in food processing and magnets are one approach that works successfully. Selecting the proper magnetic separator requires an understanding of magnetic properties, product characteristics and the specific environmental factors in each food processing plant.

Magnetic separators are available in a wide range of designs, including: bar, plate, grate, liquid line trap, pneumatic line and suspended.

• Bar magnets are permanent non-electric magnetic units that can be used in a wide range of applications. They are used to remove ferrous contaminants present in small, shallow quantities of flowing powder, granules, fibres and liquids.
• Plate magnets are used in the bottom of an inclined chute or suspended above conveyor belts or stainless steel vibratory feeders. They are used to remove ferrous contaminants that occur occasionally in products lines, particularly large pieces of metal, such as nuts, bolts or staples, from dry products.
• Grate magnets have magnetic tubes designed in a grid to allow the flow of material to cascade though a grate. They spread magnetic protection through cross-sectioned areas of equipment, such as pipes or hoppers. They can be used to remove fine or relatively large pieces of metal contaminants.
• Liquid line trap magnets are traps with tube magnets inside them, designed with an inlet port to match existing pipelines. The magnet collects metal pieces like baling wire or staples.
• Pneumatic line magnets draw metallic pieces from products such as starch, milk powder and flour as they flow through pneumatic lines.
• Suspended magnets hang above conveyor belts and remove metal fragments from the material as they pass under the magnet. They remove large pieces of metal and can protect equipment, such as crushers, from damage.

Magnet Materials

• Alnico magnets are made from aluminium, nickel cobalt and iron. They are economical magnet sources used in applications that have high temperatures (>204 °C). Alnico is comparable in strength to ceramics and is used to remove relatively large metal pieces, such as bolts or nuts.
• Ceramic magnets are low-cost and made from a composite of iron oxide and barium/strontium carbonate. They are used to remove relatively large pieces of ferrous metal such as nuts, bolts, nails and other metal objects of that size.
• Rare earth magnets generate an extremely strong magnetic field, allowing them to remove fine or weakly magnetic contamination such as rust or work-hardened stainless steel from product flow. Extensively used by the food industry, rare earth magnet types include:
  • samarium-cobalt magnets are more expensive and have a weaker magnetic field. They perform well in corrosive or high temperature environments.
  • neodymium magnets are second generation rare-earth magnets made from neodymium, iron and small amounts of boron. They are the most powerful and most affordable of the rare-earth magnets.

Factors Affecting Magnet Performance

There are several factors that can affect the effectiveness of a magnet’s performance:

• Temperature: Magnetic materials lose strength when exposed to elevated temperatures. When magnets are heated beyond certain temperatures (which depend on their specific material), they lose strength that cannot be recovered by cooling. When using magnets in a process that involves high temperatures, make sure you are using the correct material.
• Flow characteristics: Many food products exhibit different flow characteristics when damp or moist. For instance, sugar with high moisture content can form large particles that may plug the opening of a magnetic separator. This can stop the product from flowing the tubes of the magnet.
• Equipment design: The spacing and number of tubes in magnetic equipment affect the strength of the magnetic field it generates. Closer spacing and more tubes mean a stronger magnetic field and higher efficiency.
• Product characteristics: The characteristics of the food being processed greatly affect the effectiveness of magnetic separators. Food products can be categorized in three groups: dry, liquid or moist.
  • Dry products — range from small food grains flowing down a chute to large rock-like products moving along high-speed conveyor belts. Each one requires different separation equipment. If the material is small and free-flowing, a grate magnet may be best. Plate magnets do not disturb the flow of the product nor cause it to build up when it cascades down a sloped chute. Suspended magnets work efficiently when dry products are transported on a conveyor belt.
  • Liquid products — a liquid or slurry state require a magnetic trap, either in a grate or plate configuration. Traps are similar to grates, tube magnets are arranged perpendicular to the flow inside an enclosed vessel to trap any ferrous material passing through.
  • Moist products — such as flour or starch do not flow through grate magnets because of product build up. The best option is to use a powerful magnet that is completely out of the product flow. A magnetic rotation system outside the product line eliminates product build up and allows product to flow freely.

Evaluating Magnet Performance

Processors who use magnets should not take them for granted. Magnets can lose strength over time and should be tested at least once a year. Pull tests and the use of Gaussmeters are two types of measurements that evaluate magnets.

Pull Test: The pull test is an easy and repeatable test to evaluate the performance of a magnet. It measures the force required to remove a standardized piece of metal from a magnet, using a spring scale. Commercial test equipment for testing the relative strength of magnet separation equipment can be found on the market and can help monitor the efficiency of a separator by measuring the holding force of a magnet.

Gaussmeter: A Gaussmeter provides standard measurement for evaluating a magnet design.

However, it is not practical for assessing the relative effectiveness of a magnetic separator. The effectiveness (strength) depends on the magnet material but also the size and weight.

See the following fact sheet for a summary of metal detection in the food industry.

Metal Detectors in the Food Industry Fact Sheet

References

Contains information from the Government of Manitoba, licensed under the OpenMB Information and Data Use License (Manitoba.ca/OpenMB)