|McDonald's: Out to get you since 1940|
This myth is largely propagated through e-mail, but of course I have seen it on Facebook every now and then. It goes like this:
McDonalds hamburgers will not decompose, even if left on a counter for 12 years!!!1 If it won't decompose that must mean it is full of nasty preservatives and is obviously bad for you.Now, I'm not about to argue that McDonald's is good for you. A Big Mac, Fries, and a Coke will give you 1400 calories, 1.4 grams of sodium, and more fat than you want to hear about. It's not a healthy choice, but not because the burgers won't decompose.
Above is the picture you'll see most of the time. We owe this little piece of pseudoscience to Karen Hanrahan, a nutritionist who bought a burger in 1996. 12 years later, that burger (picutred left) looks almost identical to a brand new burger (pictured right). It would seem that Karen has shown that something is going on with these burgers. McDonald's is clearly up to something.
Before we solve the mystery of the zombie hamburger, let's answer this question: How does mold grow on food?
Mold needs four things to grow: Air, water, food, and a nice comfy temperature. We store our food at a good temperature for mold to grow and we keep it in dark, damp places. As you've no doubt seen, leaving food in the fridge too long is a great way to grow mold.
So why don't McDonald's hamburgers grow mold? The truth is much more boring than the tale of corporate conspiracy some may tell you. McDonald's hamburgers don't decompose because they dehydrate first.
Yup, simple as that. A dry hamburger is not enticing to mold, so it won't grow there. Try the experiment yourself. Buy two hamburgers. Place one on your counter and the other in zip-lock bag. The counter hamburger will be dry within a few hours. The zip-lock bag hamburger will retain the moisture (and, soon enough, will start growing mold). Another experiment has already been done here if you don't believe me.
If you're not quite convinced think about this. Bread will grow mold in the bag you buy it in. So why would we keep it in that bag? A slice of bread left on your counter will dry out. In 12 years it would look about the same as a slice of bread bought new from the store. It's not a bread maker conspiracy. Another example? Beef Jerky. It's dried meat that won't grow mold because it's...dried meat.
 Follow the link for my greatest pet peeve. The hamburger is reffered to as "chemical food." I have no idea what non-chemical food is. Plants contain chlorophyll, any meat contains proteins, and even a glass of water is a glass of (wait for it)...chemicals!