Reducing Metal Contamination in Food Processing
Metal in food is a serious hazard. A single fragment can injure a customer, trigger a recall and damage a brand for years. Most of that metal is iron or steel, and most of it can be removed with magnets.
This guide gives the practical steps that reduce the risk.
Where the metal comes from
Metal enters a food line in three ways.
It arrives with the raw material. Grain, sugar, flour, salt, spices, cocoa and dried fruit come from farms, mills and warehouses. Along the way they pick up nails, wire, staples, rust and pieces of broken equipment.
The line makes it. Every moving part wears. Mill blades, sieve mesh, mixer paddles, pump rotors, conveyor chains and bearings shed particles as they run. Stainless steel equipment sheds stainless particles.
People bring it. Dropped fixings after maintenance, a broken blade, swarf from a repair, a paperclip or a pen spring.
What it costs
A recall in the food industry costs far more than the product itself. There is the cost of finding and collecting the product, the lost sales, the legal exposure and the loss of trust from retailers and consumers. Metal is one of the most common causes of recalls worldwide.
Retailer audits treat metal control as a basic requirement. A line with no magnetic protection, or with separators that are never checked, will fail.
Step 1: protect the intake
Fit a magnetic separator where raw material enters the plant. A grate magnet in the intake hopper, or a plate magnet over the first conveyor, removes the large tramp iron. This protects your own mills and sieves from damage as well as protecting the product.
Step 2: catch what the line creates
Fit a separator after every stage that can shed metal. After a mill or a sieve, a grid or a drawer housing catches wear particles before they travel further. In liquid lines, a magnetic trap after the pump does the same job.
The particles created by the line are small. Standard strength magnets miss many of them. Use high strength rods of 9,500 gauss and above at these points.
Step 3: check the finished product
The last separator before packing is the most important. Everything that passes it goes to the customer. Use the highest practical strength here, and place the magnet where the product flow is thin and slow so that every particle passes close to a rod.
A magnet holds iron, steel and work hardened stainless steel. It will pass aluminium, copper and brass. If those metals are a risk, add a metal detector after the final magnet.
Step 4: clean and check the magnets
A separator only works while it is clean and strong.
- Clean on a fixed schedule. Easy clean designs let an operator strip the collected iron in a minute without tools.
- Record what is found. A sudden increase points to a failing part upstream.
- Measure the strength once a year with a gauss meter, and compare with the certificate supplied with the unit.
- Replace rods that are dented, cracked or leaking.
Step 5: control maintenance work
Most large metal fragments come from maintenance. Count tools and fixings out and back in. Clean the area with a hand magnet before restarting. Inspect sieve mesh after any work nearby.
Choosing the right separator
| Product | Typical separator |
|---|---|
| Free flowing powder or granules in a hopper | Grate or grid magnet |
| Powder in an enclosed pipe or pneumatic line | Housed drawer or bullet separator |
| Product over a sieve | Magnetic grid for sieves |
| Liquid, syrup, oil or slurry in a pipeline | Magnetic liquid trap |
| Deep bed on a belt or in a chute | Plate or chute magnet |
The SMAG range
Santosh Magnetic Works makes each of these separators in 304 stainless steel with neodymium rods up to 13,500 gauss, and supplies a tested certificate of magnetic strength with every unit. See the magnetic grids for sieves and the full separation range, or contact us to talk through your line.