It’s time to retire the sniff test; ‘smart’ food tags detect spoiled groceries in your fridge

Imagine a world where you never have to sniff a refrigerated carton of milk to see if it's gone bad.

Well... that day may be near.

Scientists have developed "smart tags" that stick to food containers and change colour when food spoils, indicating changes in temperature and bacteria levels.

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It's the latest modern-day technological gadget intended to revolutionize our kitchen habits and make our lives easier. (Egg Minder, anyone? It's an egg tray that tells you when you need to buy eggs. And let's not forget about the smart fridge that offers recipe suggestions based on what's inside.)

The 'smart' tag technology was presented this week at the annual conference for the American Chemical Society, the world's largest scientific society.

The scientists say the gel-like tags are safe, inexpensive and can adhere to beverages, canned goods, bottles and even medications to keep track of the freshness of what's inside.

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The colours indicate a range of freshness from 100 per cent fresh (red) to 100 per cent spoiled (green).

"Over time, the tag changes its colour to orange, yellow and later green, which indicates the food is spoiled," says Chao Zhang lead researcher from Peking University in Beijing, China.

Researchers tested the tags, which are about the size of a kernel of corn, by exposing milk to different temperatures until E-coli bacteria developed, eventually rendering the milk inedible.

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They hope their technology will be used by consumers as well as food manufacturers and supermarkets who need a reliable indication of shelf life for their products. The scientists suggest the tags are more effective than expiration dates because they take into account varying levels of heat exposure.