That blue disc stamped “Ferrous 25mm BST, cert number 213026B” is almost certainly a metal-detector test piece, a small certified object that food factories run through their production-line detectors to prove the equipment is still catching stray metal. What makes it odd is simple: a piece like this is a factory tool. It should never leave the production floor, let alone end up sealed inside a finished bag of crisps.
So the mystery isn’t really “what is it.” It’s “how on earth did it get in there.”
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What a Metal-Detector Test Piece Actually Is
On most food lines, product passes through a metal detector or an x-ray inspection system before it gets packed or shipped. The machine is supposed to spot and reject anything containing metal above a set size. Think blade fragments, wire, or a bolt that worked loose from the equipment.
But a detector is only
