When it comes to buying packaged meat and fish, consumers usually just have to go by the "best before" label to know that it hasn't begun to spoil. Needless to say, the dates on those labels are just estimates and certainly won't tell you if the product has sat through a lengthy power failure, or been left out of the cooler for several hours. Researchers from the Fraunhofer Research Institution for Modular Solid State Technologies in Munich, however, have developed an inexpensive plastic film that will change color in the presence of rotten foods.

The film would be applied to the inside of food packaging, where it would respond to the biogenic amines produced by decaying meat or fish. If a sufficient amount of amines were present in the air within the sealed packaging, they would cause dye in the film to turn from yellow to an obvious blue.

A gas-permeable layer in the film would allow the amines to reach the indicator chemicals, while not allowing those chemicals to come into contact with the food.

The Fraunhofer scientists are also designing handheld measurement modules incorporating the film, that employees at places such as meat packing plants could use to check foods while still on the production floor. They are now looking for industry partners, in order to commercialize the film.

This is not the first – or even the second – time that such a product has been developed. A team from Scotland's University of Strathclyde announced their own color-changing freshness-indicating plastic film just this January, while Canada's Toxin Alert has been working on a similar technology since 2000.