Periodically, over the last year, I've wasted a day or so screaming at my computer screen about how photos of a McDonald's hamburger failing to rot were not a sign that the food was somehow artificial or dangerous, but, rather, just what happens to meat products and bread when you leave them out in the open air. Think about the last hunk of baguette you didn't finish. Same thing. Basically, the food dries out before it has a chance to rot.
I'd been concocting a scheme to try this out at home, pitting a McDonald's burger against one made at home from free-range beef and organic bread. Luckily for my husband, Serious Eats up and did what I'd merely threatened.
In the picture above: A real,
live rotting McDonald's hamburger. Notice the plastic bag, which traps moisture and prevents the burger from drying out before the mold sets in.
Interestingly, because he ran this experiment with an impressive level of thoroughness, J. Kenji Lopez-Alt figured out that large McDonald's burgers (as opposed to the single-patty Happy Meal size) will, in fact, rot in open air. As will home-made burgers of similar proportion. It's only the small ones that get mummified. His conclusion:
The burger doesn't rot because it's 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. It's not really surprising. Humans have known about this phenomenon for thousands of years. After all, how do you think beef jerky is made?
Read the full experiment (includes graphs!) at Serious Eats