Now Lasers Can Tell You When Fruit Is Ripe

I love avocados, but I'm never in tune with their schedule. I'm really excited to eat them when they're still too hard, so I wait for a few days. But the next thing I know they're all mushy and black, barely salvageable. Time after time, I sadly watch my $2 go into the trashcan.

Researchers in France and Lebanon have invented a device that allows fruit farmers or connoisseurs to detect a fruit's peak ripeness based on how lasers interact with a fruit's outer layer of cells, which physically change as the fruit ripens. The device is designed to be affordable enough for farmers to use with their crops, according to a study published Wednesday in Applied Optics.

Fruits ripen in two different ways: on the vine and off the vine. Climacteric fruits, ones that ripen off the vine, like apples, pears and bananas, regulate their maturation with the hormone ethylene. Plants emit the hormone as a gas, which has a number of effects on the cells of the ripening fruit: softening of cell walls, changes in the fruit's color, and usually more sugars and fewer acids. Not only does this happen at different rates in different types of fruit, it can vary within the same type of fruit.

The cells of a fruit at different stages of ripening react differently to high-intensity light; when researchers illuminate a fruit with a laser, a process called biospeckling, they can correspond the resulting image of cell patterns to the stage of the maturation process by developing a standard.

In the new study, the researchers developed a device that is able to make these images cheaper and more efficiently. To detect the ripeness of a golden delicious apple, they shot a laser through a few lenses to give the light the right spin and wavelength, and hooked up a digital camera to take a picture of the cell patterns.

"A group of sparkling and dark grains called 'speckle grains' make up this pattern. If the medium is biological—meaning that it presents some sort of cell activity—its speckle pattern will show changes with time," said Rana Nassif, a postdoc in physics at Université de Bretagne Occidentale in Brest, France, in a press release. "And this pattern depends on the medium's scattering properties, as well as its own nature."

The device isn't yet ready to hit the shelves, but the researchers hope that farmers will be able to use it in the future so they can harvest their crops at the perfect time. "Simplicity and low cost are the key advantages of our technique," Nassif said. Hopefully they'll come out with one simple enough for the rest of us to use, too.