A surefire way to tell if your food has gone bad

Todd Korol/REUTERS/File 2013

As meat sits in your refrigerator, the dilemma inevitably arises: Should you take your chances with off-color ground beef or err on the side of caution and throw it away? Regardless of what you choose, you’re likely to wish you had better information with which to make the decision.

Researchers at the Korea Advanced Institute of Science and Technology, or KAIST, may be on to a solution. Thanks in part to a puzzling result in an unrelated lab experiment, they’re developing technology that could allow anyone with a cheap laser pointer and a smartphone to quickly assess the bacterial content of food.

“All you need is a laser source and an image sensor like a camera,” says YongKeun Park, a professor of physics at KAIST and co-developer of the device. “Imagine if you buy chicken breast and place it inside your refrigerator, what if your refrigerator could warn you, don’t eat this.”


The technology uses a technique called laser speckle imaging. If you shine a laser at a surface, the light that’s not absorbed will bounce back toward you. It won’t bounce back in exactly the same form as it arrived, however. Due to irregularities in the surface, the photons will return along different path lengths, which interfere with each other when they reach a lens (like your eye or a camera). Some paths will augment each other, creating bright spots, and some will cancel each other out, creating dark spots. The result is a telltale speckle pattern.

“You can actually use the properties of that speckle pattern to figure out the roughness of the surface,” says David Boas, a professor of radiology at Harvard Medical School who in 2001 found a way to use the technique to map blood flow in the brain. Other applications use laser speckle imaging to understand how tumors respond to chemotherapy.

Last year, the researchers at KAIST were using laser speckle images to try to re-create the path that scattered light had traveled after reflecting off a surface. The surface they chose to use was chicken breast tissue. But when they ran their experiment, they observed that the speckle patterns were inconsistent from one day to the next, even when the same light source was reflected off the same chicken breast tissue. They quickly figured out that this was because the surface was changing.


“Because we stored the chicken breast tissue at room temperature, it had been rotting, which means the contaminated chicken breast tissue had more moving particles,” says Park.

Those moving particles were bacteria. Park and his colleagues realized that the way the speckle pattern changed from one instant to the next provided evidence about the concentration of bacteria on the chicken breast tissue. The chain of reasoning is similar to the one applied with the Doppler effect. There, an observer can calculate the velocity of a moving object based on how the frequency of a sound changes when the sound waves hit the object, scatter, and bounce back. In the case of a laser reflected off of food, the way the speckle pattern changes over time provides evidence of the presence and activity of bacteria.

By analyzing those changes, researchers can begin to determine the amount of bacteria that have collected on the surface. “The application [of laser speckle imaging] to food is wonderful,” says Boas. “The speckle pattern begins to fluctuate in time because the scattering particles, in this case the bacteria, are moving within the tissue.”

Since posting their research as a preprint in March, Park and his colleagues have been contacted by several companies in the food industry that are interested in implementing this method in their factories and refrigerators. There are still some kinks to be worked out. In particular, the researchers need to find a better way to quantify changes in the speckle pattern over time and then refine the relationship between those changes and the level of bacterial contamination. If they achieve this, the safety of the food in your refrigerator would no longer be a matter of guesswork — though you still might have to convince yourself that those mealy shrimp are safe to eat, just because your laser-equipped phone says so.


Kevin Hartnett is a writer in South Carolina. He can be reached at kshartnett18@gmail.com.