Ripe fruit

Fruit wholesalers deliberately expose green bananas or tomatoes to ethylene to make them ripen faster, causing the fruit to develop the typical yellow or red colour that their customers expect.

Conversely, the wholesalers keep the ethylene concentration in the warehouses low if the fruit needs to stay fresh for a long time.

If too much ethylene is pumped into the fruit warehouses, the bananas turn brown and overripe. But if too much gas is extracted from the refrigerated halls, a large amount of cool air also escapes, unnecessarily wasting energy.

Now, a new sensor has been developed at the Fraunhofer Institute for Physical Measurement Techniques in Freiburg that could help warehouse managers measure the ethylene concentration accurately at a low cost.

'This sensor is much more compact and also much cheaper than traditional complex measuring systems. At roughly €1000, it costs only about a tenth of the price,' said Dr. Jürgen Wöllenstein, team leader at the Institute.

He and his team developed the sensor in collaboration with colleagues from the University of Barcelona. Its core components are an infrared radiator which emits radiation of different wavelengths, and a filter that only allows radiation with a wavelength of 10.6 micrometres to pass through. The filter is necessary because ethylene absorbs radiation of this wavelength. The more ethylene is present in the air, the less radiation reaches a detector which is integrated in the sensor.

A prototype of the sensor already exists. In about two years from now, it could be helping fruit wholesalers control the amount of ethylene they use in their warehouses.