In order to be safe to eat, raw products made from ground beef must be cooked until they are at least 71°C in the centre. However, it can be difficult for consumer to measure the temperature during cooking.

Meat package in oxygen-rich atmosphere has a much more intense red colour the first few days after packaging, however the colour in the centre of a hamburger cannot be used to decide whether it is throughly cooked or not. Because meat packaged in an oxygen-rich atmosphere looks cooked already when it reaches 60°C.  

– And we know from former studies that people use colour as an indicator for cooking, says Solveig Langsrud.