After a rigorous scientific test, the results are in. McDonald's burgers don't decay, but neither do home-made patties of freshly ground chuck steak.
Kenji Lopez-Alt, an MIT-trained chef who's behind the very smart blog The Food Lab (and a forthcoming book by the same name), dug into one of the most perplexing and disturbing questions that's been buzzing around the Internet: Why did that McDonald's hamburger not decay for over 137 days?
There's been speculation that the meat was pumped full of chemicals and sodium propionate, but Lopez-Alt wanted an objective test so he set up an informal experiment. He left the burger out, unwrapped, and he also made his own burger out of ground chuck, salted and cooked it (just like McDonald's), and put it on a store-bought bun and left that out, too.
What happened? It turns out that neither burger decayed.
The burger doesn't rot because [its] small size and relatively large surface area help it to lose moisture very fast. Without moisture, there's no mold or bacterial growth. Of course, that the meat is pretty much sterile to begin with due to the high cooking temperature helps things along as well.
So there you have it, meat and heat goes a long way in preserving things. Whether this means you should go out to Mickey D's or challenge some long held assumptions about leaving meat lying around your house is entirely up to you. Personally, I would recommend either checking out this recipe or reading another great post from The Food Lab.