Infra-red sensor tunes fruit ripening


The Fraunhofer-Institut fur Physikalische Messtechnik in Germany has built a gas sensor to control fruit ripening.

“Particularly bananas give off a lot of ethylene, which causes the apples to ripen faster,” said the Institute. “Wholesalers make use of this effect, actively regulating the ethylene concentration in fruit warehouses.”

The team is using infra-red spectrometry to under-cut existing techniques.

“This sensor is much more compact and also much cheaper than traditional complex measuring systems,” said team leader Dr Jurgen Wollenstein. “At roughly a thousand Euros, it costs only about a tenth of the price.”

At the core of Wollenstein’s detector is an infra-red radiator “optimised to emit as much heat as possible at the appropriate wavelength” and 10.6[micro]m pass filter. “The filter is necessary because ethylene absorbs radiation of this wavelength,” said Fraunhofer.


The more ethylene is present in the air, the less radiation reaches the detector – a similar method is used for monitoring CO2.

“The challenge with ethylene is its extremely long wavelength. We had to ensure that the radiation could travel a very long distance through the air, as this is the only way we can reliably measure the effect and thus the ethylene concentration,” said Wollenstein.

To reduce the size of the sensor, its 3m optical path is folded by to “the size of a box of cigarettes” by gilded mirrors.

A prototype of the sensor already exists and is expected to be in use in about two years.

Fraunhofer is partnered with the University of Barcelona for this programme.

Tags: control

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