Ethylene monitor for use in fruit warehouses

Licensing Opportunity, Development Opportunity

Ethylene causes fruit to ripen and wholesalers make use of this effect, exposing green bananas or tomatoes to ethylene to make them ripen faster. Conversely, they keep the ethylene concentration in warehouses low if fruit needs to stay fresh for a long time.

Fine tuning is required for both processes: too much ethylene will turn bananas brown and overripe. But in extracting ethylene from refrigerated halls a large amount of cool air also escapes, wasting energy.

Now a German/Spanish research team has developed a sensor that can measure ethylene concentrations accurately at a low cost. “This sensor is much more compact and also much cheaper than traditional complex measuring systems, says Jürgen Wöllenstein, team leader at the Fraunhofer Institute for Physical Measurement Techniques (IPM) in Freiburg. “At roughly a thousand euros, it costs only about a tenth of the price.” A prototype sensor has been produced, and the team believes it could be commercialised within the next two years.

Wöllenstein and his colleagues developed the sensor in collaboration with researchers at the University of Barcelona. Its core components are an infrared radiator, similar to a heat radiator, which emits radiation of different wavelengths, and a filter that only allows radiation with a wavelength of 10.6 micrometers, the only wavelength at which ethylene absorbs radiation, to pass through.

The more ethylene is present in the air, the less radiation reaches the detector, which is likewise integrated in the sensor. This method of measuring gas concentration is already in use for monitoring carbon dioxide.

“The challenge with ethylene is its extremely long wavelength of 10.6 micrometers. 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,” explains Wöllenstein.

The researchers deflect the radiation with gilded mirrors to make it cover a distance of over three metres inside a sensor the size of a box of cigarettes. The scientists have also optimised the infrared radiator to emit as much heat as possible at the appropriate wavelength.