A simple plastic disc designed to sit inside food packaging changes colour when exposed to the noxious vapours given off by rotting food. Its developers hope it will provide a simple way for consumers to tell whether food has gone off.

Dwight Miller and his colleagues at the US National Center for Toxicological Research in Jefferson, Arkansas, created the polymer discs. They contain complex organic dyes that change colour drastically from clear to telltale pink, blue or yellow, depending on the type of food. Reference colours printed on the packaging will let people judge if food has gone bad.