Spoiler Alerts

Family refrigerator. Christopher Anderson/Magnum

With the jumble of "use by," "best by" and "sell by" date labels, it's hard to keep track of whether that jar of mayonnaise lurking in the back of your fridge is going to rock your chicken salad or kill you. And throwing out food past the date on the label can add up: A typical American family of four wastes hundreds of dollars a year due to date-label confusion. But a new color-coded, temperature sensitive food label could help cut down on waste.

Chao Zhang, a researcher at Beijing University in China, has created a smarter label, one of a new class of technologies called time-temperature indicators. Zhang's popcorn-kernel-sized tags are made of gel and contain gold and silver nanorods. They are engineered to change color over time at the same rate that the food inside spoils, tracking the decline of freshness along the way. "You can always know if the food is good or bad, just by simply reading the tag color," Zhang says. The tags can be stuck on the outside of the food packaging and cost far less than a penny.

A green smart tag indicates that the product is no longer fresh. Sean Parsons/American Chemical Society

The labels can also account for the changes in temperature that happen on the way from farm to fridge. This is one of the biggest challenges in keeping food fresh, says Dana Gunders, a staff scientist at the Natural Resources Defense Council. Any amount of time food spends in the "danger zone"—between 40 and 120 degrees—enables bacteria to grow more quickly, which can lead to spoiling. "If you buy milk, meat or greens, and let them sit in a hot car for four hours, the date on that product is essentially rendered meaningless because you've mishandled that product," she says. Manufacturers have to account for this when labeling food, leading them to make conservative guesses for how long a product will keep. Better labels would reduce the uncertainty, keeping fresh food in your fridge—and out of your trash.