Pittsburgh’s Lauren Wallace is willing to go the extra mile to make sure she’s getting the freshest milk possible at the grocery store. She regularly inspects the sell-by dates on the cartons and even digs to the back of the cooler to get the best ones. And when the milk in her fridge hangs around beyond the expiration date, she doesn’t even give the milk a chance to make a case that it’s still viable.
“I automatically dump it,” Wallace says. “I wouldn’t even taste it.”
Wallace isn’t alone. According to Harvard Law School’s Food Law and Policy Clinic, 90 percent of us throw food away—either always, most of the time or occasionally—when that sell-by date arrives. But what many consumers don’t realize is that those dates aren’t intended to be hard-and-fast deadlines.
“They’re a guess by the manufacturer when they think the food will not taste as good or not be at its top quality,” says Emily Broad Leib, the director of the Harvard Law School Food Law and Policy Clinic. “They’re not intended to communicate safety.”
Broad says there is no standardization for sell-by dates—they vary by company and state. Pennsylvania is one of the strictest states when it comes to sell-by dates on milk: It has to be within 17 days of the date the milk was pasteurized. Milk can’t be sold after that, so it’s either thrown or given away. The policy isn’t about food safety. The Pennsylvania Department of Agriculture says it’s a quality issue.
But a physics professor at Indiana University of Pennsylvania thinks he’s accidentally hit on a better way to tell how fresh your milk really is. Greg Kenning and his students were working on a completely different project that involved embedding magnetic nanoparticles of the metal cobalt into the semi-metal antimony. And they noticed some interesting things about the magnetic and electronic properties of these elements as they decay with time and temperature.
“The decay properties were very similar to the decay properties of food,” Kenning says. “This was a pure discovery. We weren’t looking for this.”
Now, Kenning and his students are cranking out samples of these metals to learn more. Using an instrument called an electron beam evaporator, Kenning first shoots electrons at a small square brick of antimony. This heats up the surface of the metal, which causes the antimony to evaporate.
It then rises and beads up on a silicon chip, forming a thin layer. Kenning and his students repeat this process over and over, creating multiple layers of the metals. And it’s these super-thin metal films that could one day be embedded in a label on a milk carton—mirroring how the milk inside is aging.
Kenning is now working with the Massachusetts Institute of Technology (MIT) to combine the films with Radio Frequency Identification (RFID) technology—the same kind of technology E-ZPass transmitters use to wirelessly relay information on toll roads. The concept is that electronic devices could then read information about a product’s freshness stored on the RFID-equipped label.
“So the idea is that you would come in to buy your quart of milk, and instead of looking at the dates for the freshness, your cell phone would tell you what the freshest milk was in the whole system,” Kenning says. “You’d have a scanner in your fridge. Your fridge would tell you when it’s going to expire.”
Kenning thinks the labels could be made for pennies a piece but that the information will be invaluable to consumers. He says it could help keep the supply chain honest, because it will be easier to tell if milk has been left out or improperly refrigerated on its way to the store. And it could also help reduce food waste.
“If you know your milk or your meat’s got a day, day and a half, and you’re getting an update on it, you go, ‘Oh, OK, we’re going to use that meat today,’” Kenning says.
Once Kenning and his team have milk nailed down, they plan to develop sensors for other types of foods—fine tuning their samples to track different rates of decay. He says his milk sensors could appear in a grocery store near you within a couple of years. Until then, you’ll still have to use the sniff test to tell if that milk is worthy of your cereal.
This story was produced by The Allegheny Front, a public media group covering the environment in Pennsylvania.