Smart tags to consign use-by dates to the scrap heap

ELECTRONIC tags could soon replace traditional use-by dates on food, allowing people to see precisely when perishables items are about to go off.

Chinese food scientists have produced a new label – known as a smart tag – that shows how much life is left in food, rather than relying on manufacturers' estimates. The technology will take the guesswork out of food consumption and could help to cut waste, say the inventors. Use-by dates are known to err on the side of caution, rather than accurately reflecting when a product has gone bad.

The system was demonstrated at a meeting of the American Chemical Society in Dallas, Texas. The colour-coded smart tags are designed to be placed on the packaging of a perishable product and will change colour to indicate the freshness of its contents.

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"In our configuration, red, or reddish orange, would mean fresh," explained Chao Zhang, the lead researcher of the study. "Over time, the tag changes its colour to orange, yellow and later green, which indicates the food is spoiled."

The tags contain tiny metallic "nanorods" made of gold and silver. These small rods mimic the degradation of food by undergoing a gradual chemical reaction which causes the traces of silver to deposit on the gold rods. This in turn causes the smart tag to change colour, The Times explains.

In spite of being made of precious metals, Zhang says the tags would be very cheap to produce, costing less than a penny each.

The patented technology is yet to be adopted by manufacturers.