Serious Eats’s Kenji Lopez-Alt investigates exactly why those McDonald’s hamburgers didn’t decay over 137 days. The assumption, of course, is that McDonald’s pumps their food with so much chemicals/preservatives that they couldn’t possibly rot.
Lopez-Alt conducted a little experiment using an unwrapped McDonald’s burger and made his own burger out of ground chuck, salted it liberally, cooked it (similar in method to McDonald’s), and put it on a store-bought bun and then left it out, as well.
Surprisingly, 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.
Huh. Honestly, I’m at a loss for words. . . So there you have it, McDonald’s is okay to eat! But seriously, I would be dubious, but Lopez-Alt puts a tremendous amount of food science into his findings and it’s hard not to be persuaded by his conclusions.