Is duck safe when cooked medium-rare? Not according to the Food Standards Agency (FSA) it isn’t.
As the FSA continues to focus on Campylobacter – the UK’s leading bacterial cause of food poisoning – last week they reiterated their advice that all poultry should be cooked through, and even duck cannot be safely eaten medium-rare. Recent studies have shown Campylobacter is found on 50% of duck meat and an FSA spokesperson has said “the FSA’s advice is that duck and other poultry should be cooked until steaming hot throughout and until there is no pink meat left”.
This advice is problematic on many levels; it’s simplistic, it ignores that overcooked duck possesses the flavour and texture of shoe leather but none of its utility – and it demonstrates a lack of understanding of basic food science. Colour is not a reliable indicator of ‘done-ness’ and every time the FSA publishes daft advice it marginalises itself with the very people it seeks to influence, as well as giving the wrong signal to the enforcement community.
Campylobacter is the leading bacterial cause of food poisoning in the UK, making over 280,000 people sick and hospitalising 20,000 per year. In the majority of cases its carriage is usually attributed to chicken, where campy is one of the ‘normal flora’ living in the chicken gut. It is a problem, it makes a lot of people sick, it has a low infectious dose but you can’t get rid of it, even were the industry to implement impractical levels of hygiene or by feeding flocks huge amounts of antibiotics – which would cause other problems.
So, this is an organism that’s naturally endemic in poultry, but like most bacteria that get into the food chain it is generally found on the surfaces of meat, not in the meat itself. Prevention of contamination by resident bacteria that can be harmful to consumers is not helped by the way poultry is processed: how it is transported, the stunning process where birds are dunked in what is – from a microbiological perspective – a bath of tepid faeces, the evisceration process and also the temperature at which carcasses are subsequently scalded all play their part.
And yes, there are exceptions to the ‘on, not in’ rule: some organisms do colonise muscle – nematode worms like Trichinella spiralis for example, or Hepatitis E in pork – but these are very much the exception, certainly in the UK. So, for all sorts of reasons you can’t really escape bacteria – including campy – being on the surface of meat. Hence the advice to cook thoroughly and as a minimum ensure the surfaces are well-seared.
But what’s the difference between a duck breast that’s pink in the middle and a medium-rare steak?
Let’s get down to basics. There are two really good ways to kill microorganisms: chemicals and heat. Dunking food in bleach before cooking doesn’t do much for the taste so we tend to rely on heat to kill any bugs travelling on food. Different bugs take different amounts of time to kill at different temperatures, for example at 60°C it takes about a minute to kill 99% of Salmonella – depending on a few variables. The higher the temperature, the shorter the kill time. These values are well-charaterised for relevant bugs at different temperatures and are known as ‘D-Values’ – the time it takes at a given temperature to kill 90% of a particular organism. For Campylobacter jejuni it’s just over a minute at 55ºC. So a minute at that temperature gives a 90% reduction, two minutes 99% and so on. There is variation and to give you an idea campy is rapidly inactivated by heating at 55°C and above: the D-Values are D50C= 1 – 6.3 min, D55C = 0.6 – 2.3 min, D60C = 0.2-0.3 min.
But that’s only half the story. What the FSA don’t seem to appreciate is that meat colour is a rubbish indicator of ‘done-ness’. Or that most people are quite capable of using a meat thermometer. Red meat such as beef, lamb and duck can get up to adequate temperature to kill bugs but still be pink. As can a turkey or duck leg. Here’s why.
It all comes down to what happens to various molecules found in meat as it cooks: at 50°C myosin coagulates and goes opaque – which is obvious in chicken or fish but will also lighten red meat to pink. Give it ten degrees more and myoglobin oxidises into molecules called hemichromes and the meat goes from pink to brown / grey. These bind to other proteins which is why juices from cooked meat run clear. So, a duck breast that’s well-done and crispy on the outside but pink in the middle is highly unlikely to present any risk, provided the internal temperature is sufficient.
But there are other oddities to how myoglobin behaves, again showing you can’t always tell done-ness by colour. For example if you slow-cook red meat it can still appear pink inside because by the time the myosin and cytochrome pigments have reached the temperature at which they unravel, all the other proteins have already denatured. This means the pigments stay red because all their potential playmates have already done any reacting they’re going to so there’s no-one left for the pigments to bond with.
And if you’ve ever wondered why when barbecued the surface of meat sometimes stays pink (to a few mm depth) this is because the nitrogen dioxide (NO2) given off by wood or charcoal turns into nitrous acid (HNO2) at the surface which turns into nitric oxide (NO) in the tissues. This reacts with myoglobin to form a stable, pink molecule.
So, as usual generalisations are difficult. Is pink duck meat completely risk-free? No. Nothing is risk-free. And statistically even if you burn all your food to a crisp you are still 100% likely to die. But if you like your duck medium-rare – and who wouldn’t – buy a digital thermometer.