It’s not like a steak
You can have your steak rare but it’s a common mistake to think that burgers, because they are also made from beef, can be served pink. Burgers aren’t like steak, even 'upmarket' versions which are described as 'steak burgers'.
Contamination of meat with harmful bacteria such as E. coli O157 and Salmonella can occur when meat is produced. When cattle are slaughtered there is potential for the pathogens from the animal’s gut and hide to contaminate the surface of carcasses during the slaughter and preparation of the meat.
Contamination of whole cuts of beef like steaks and roasting joints tends to be only on the outside of meat, so cooking the outside and leaving the middle rare is safe. However, the mincing of raw meat and forming into burgers will spread any bacteria present on the surface of the meat throughout the burgers. If harmful bacteria are present in the middle of the burger and that part of the burger is not thoroughly cooked, bacteria can survive and cause illness.
Cooking - time and temperature
When you’re cooking food, it’s important to think about the time and temperature of cooking. Cooking causes the transfer of heat energy into food and that energy breaks down proteins in the food – this change in the structure of proteins is part of the reason meat changes in texture and in colour from pink to brown.
It is also this effect that can kill harmful bacteria. Although bacteria need heat and energy to grow, this typically happens between 8°C and 60°C; below 8°C, growth is stopped or significantly slowed down and above 60°C the bacteria start to die. Cooking also causes the proteins in bacteria to break up. It requires a certain amount of energy to build up and cause the reaction that breaks up the protein structure, which is why time and temperature are both important – proteins need to be heated up for a long enough time for all of them to be broken down.
Burgers in restaurants
Some restaurants are able to put in place strict controls right from the start of the process to prevent or reduce contamination on the meat they use for burgers. This includes specific, scientifically validated cooking methods in the restaurant that mean that the risk from burgers that are pink in the middle is significantly reduced. This isn’t the case for all the meat that reaches supermarkets, butchers and other shops though, which is why you should only eat burgers that are pink in the middle in restaurants that have these strict controls in place.
You should also remember that there is still some risk involved whenever a burger isn’t thoroughly cooked, even in restaurants with strict controls in place, so we advise that children and anyone who is more vulnerable to food poisoning such as the elderly, pregnant women and people with a weakened immune system, should only ever eat burgers that are thoroughly cooked all the way through.