A spice plant should have magnets on the raw material and powder lines, a check sieve after grinding that every batch passes through, and a metal detector on the finished product. Each control must be checked and recorded at fixed intervals.
The equipment matters less than the routine around it. A detector that is never tested, or a torn sieve that nobody inspects, gives no protection.
Magnets
Strong magnets, often rare-earth types, sit in chutes, hoppers and pipelines. One set before the mill protects the grinder from tramp iron. Another after grinding catches fine iron particles from wear.
Magnets catch only magnetic metal. They should be cleaned on a schedule, and what they collect should be recorded. A rising amount of fine iron is an early warning that a mill part is wearing.
Sieving
A check sieve after grinding removes oversize particles, lumps and some foreign bodies. Its mesh follows your particle size specification, as discussed in mesh size for spice powders.
Screens should be inspected for tears every shift and at every product change. A torn screen lets everything through, and a damaged wire screen can itself shed metal. The tailings, meaning what the sieve rejects, are worth looking at: they show what the raw material and mill are putting into the product.
Metal detection
- The detector should be set to find ferrous, non-ferrous and stainless steel. Stainless is usually the hardest to detect.
- It is tested with certified test pieces of each metal type. The sizes are set by the plant's validation and your customer's requirements, not by a universal standard.
- Tests happen at start-up, at fixed intervals, at product changes and at the end of a shift.
- Rejects go automatically into a locked bin, and each reject is investigated.
- Sensitivity falls as pack size grows, so detection is more effective on smaller packs, or on a pipeline unit before filling large bags.
- Some buyers ask for X-ray inspection, which can also find dense foreign bodies such as stone and glass.
What to ask to see
Records tell you more than the machines. On an audit or before a first order, ask for:
- The test piece certificates and sizes for each detector.
- The last month of detector test logs, with the operator's signatures.
- The reject log and what happened to rejected product.
- Sieve inspection logs and the date of the last screen change.
- Magnet cleaning logs and the record of what was found.
- What happens to product made since the last good test if a detector fails a test.
How we help
When we audit a spice plant, we watch the metal detector being tested, inspect the sieves and magnets, and read the logs. For a wider view of contamination control, see avoiding foreign bodies in spice powder, or ask for a free sourcing review.