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Sensor tests fruit for ripeness, cuts waste

Image of fruit at a grocery store
A new sensor technology developed at MIT may help grocery stores reduce the amount of spoiled fruit they throw away.MIT

To the chagrin of Dumpster divers everywhere, grocers may soon have sensors that accurately measure fruit ripeness, helping them reduce the amount of produce they throw away due spoilage on store shelves.

Grocery stores lose about 10 percent of their fruits and vegetables to spoilage every year, according to statistics from the U.S. Department of Agriculture. Even perfectly good food gets tossed out at closing time because it will be spoiled by morning.

While the tossed good stuff is a boon to late-night Dumpster divers, it hurts the bottom line of grocers and is likely factored into the price shoppers pay at the checkout stand.

The new sensors can detect tiny amounts of ethylene, a gas that promotes ripening in plants. In theory, they will let grocers know far enough in advance to put soon-to-spoil food on sale, clearing it from the aisle without putting it in the trash bin. 

The technology is based on carbon nanotube sensors designed to detect explosives or chemical and biological warfare agents.

Timothy Swager, a chemistry professor at the Massachusetts Institute of Technology, and his students modified these sensors by adding copper atoms to the tubes. This slows the flow of electrons over the tubes and, when ethylene is present, it binds to the copper atoms and slows the electrons even more.

“By measuring how much the electrons slow down – a property also known as resistance – the researchers can determine how much ethylene is present,” MIT explains in a news release

The ethylene sensors are also fitted with beads of polystyrene, which absorbs the tell-tale gas and concentrates it near the bottom of the tubes, which increases sensitivity. 

In lab tests, the team was able to detect concentrations of ethylene as low as 0.5 parts per million. Concentrations for fruit ripening are between 0.1 and 1 part per million.

Swager envisions the sensors attached to cardboard boxes of produce that communicate wirelessly via an RFID chip that is scanned with a handheld device. The sensor would cost about 25 cents and the chip another 75 cents.

Given that the technology has already proven successful at detecting ripeness for high-value fruits such as avocados, which can cost more than $2 each in Seattle-area stores, the investment seems worthwhile.

For more information on the sensor, check out a paper describing it published in the journal Angwandte Chemie

John Roach is a contributing writer for To learn more about him, check out his website and follow him on Twitter. For more of our Future of Technology series, watch the featured video below.