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Using your smartphone to find out if your milk has gone bad

Flickr user tmray02/Flickr

How do you decide if your milk is fresh enough to drink? You might be one of the many Americans who relies on sell-by dates to determine when to throw it out. But it turns out we could be dumping perfectly good milk. 

A physics professor thinks he’s hit on a better way to tell if food is fresh. And he’s taking it to market.

Are sell-by dates widely misunderstood?

It’s Saturday morning at a grocery store near my house. Lauren Wallace is inspecting quarts of milk from the back of the cooler for the latest sell-by date. She trusts it, and when the milk in her fridge hangs around beyond that date...

“I automatically dump it — I wouldn’t even taste it,” she says.

Wallace is not alone.

“Basically, around 90% of people throw food away when that date arrives, either always, or most of the time, or occasionally,” says Emily Broad Leib, director of Harvard Law School’s Food Law and Policy Clinic.

Leib says what most people don’t know is those sell-by dates have no standard meaning. They vary by state and even by company.

“They’re a guess by the manufacturer when they think the food will not taste as good or not be at its top quality,” Leib says. “They’re not intended to communicate safety.”

That’s right — a guess.

So what if there were a more accurate way to tell if milk is fresh inside the container?

Discovering a potential replacement for the sell-by date

Greg Kenning, a physics professor at Indiana University of Pennsylvania, wasn't setting out to make a new discovery. He and some of his students were just minding their own business, experimenting in the lab.

Credit Kara Holsopple/The Allegheny Front
Greg Kenning's discovery of a new way of detecting food freshness was completely accidental. "This was a pure discovery. We weren't looking for this," he says.

“We weren't looking for this,” Kenning says. “What I really wanted to make was what was called a super spin glass.”

Don’t panic, for those of us who aren’t physicists, all you need to know is they were working with two elements. Remember your periodic table?

Kenning embedded magnetic nanoparticles of the metal cobalt into the semi-metal antimony.

“One nanometer usually is about three atoms wide,” Kenning says.

The elements changed with time. Kenning increased the temperature, and noticed something really interesting: decay of their magnetic and electronic properties.


“The decay properties were very similar to the decay properties of food,” Kenning says.

Now he and his students are cranking out samples to learn more.

From the laboratory to the grocery store

"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." — Greg Kenning, physics professor at Indiana University of Pennsylvania

We’re in his lab, standing in front of an electron beam evaporator. It’s like a big bell jar. Kenning twists a knob so that inside the cylinder, a little square brick of antimony is placed into the path of a gun that drives electrons over it.  

“It just heats up the surface of the metal. So it’s only the metal that evaporates,” Kenning says.

It rises and beads up on a silicon chip, forming a thin layer. Kenning and his students do this over and over, creating multiple layers of the metals.

These little samples, films of metal, like ultra-thin aluminum foil, could one day live 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.”

He thinks the labels could be made for pennies a piece.

And they might also reduce waste.

“Because if you know your milk is, or your meat is going to — it's got a day, day and a half, and you're getting an update on it. You go, ‘Okay, we’ve got to use that meat today.’ As opposed to leave it for two days and throw it away,” Kenning says.

Once Kenning and his team have milk nailed down, they’ll move on to 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.

You can take a look at https://vimeo.com/157746427">this video for more on Kenning's discovery.

Kara Holsopple hosts and reports for the environment news program, The Allegheny Front.