A scanner that analyses the wavelengths green tomatoes bounce back can predict those that ultimately will ripen, Frederico Hahn of the Centre for investigation of Food, Sinaloa, Mexico, has shown. "Maybe you can find some clues that ripening will happen," agrees Ian Young who is working on similar detectors at the Delft University of Technology in the Netherlands. Like Hahn, fruit sorting company Colour Vision Systems, in Bacchus Marsh, Australia, uses infrared spectroscopy to measure the sugar content of melons and stone fruit. The technology could be adapted for tomatoes, concedes one of their scientists Gary Brown. Some fruit packers already use automatic colour sorters to grade the ripeness of their fruit. Conventional cameras measure red, green and blue wavelengths emitted, and classify the produce before boxing. The United States Department of Agriculture has six official colour classification: green, breaker, turning, pink, light red and red.

But to these cameras, one green tomato looks like another. So size, shape and internal appearance are used to judge when a green crop is on the turn. Hahn's sensor instead measures all wavelengths over a large part of the visible and invisible spectrum.

Fruit that never ripen emit more intensely at some infrared wavelengths on day one, he found. The green pigment chlorophyll has a characteristic emission of infrared light that changes during repining, as chlorophyll degrades and red and yellow pigments called carotenoids accumulate. Hahn used these key wavelengths to develop a ripeness predictor.