Could the sniff test for rotten milk be a thing of the past? Scientists at Washington State University developed a sensor that can “smell” if milk has gone bad—without opening the package.

The sensor changes color when its chemically coated nanoparticles react to gas and bacterial growth that indicate spoilage, says Shyam Sablani, a professor in the Department of Biological Systems Engineering. The sensor doesn’t touch the milk directly.

“If it’s going bad, most food produces a volatile compound that doesn’t smell good,” Sablani says. “That comes from bacterial growth in the food, most of the time. But you can’t smell that until you open the container.”

So far, Sablani and his colleagues showed that the chemical reaction works in a lab, publishing their findings in the journal Food Control.

Now the team wants to expand the technology to show how long a product has before it spoils. Sablani envisions the sensor getting integrated in a milk bottle’s plastic cap. It could be more accurate than an expiration date.  

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