Culinary raconteur J. Kenji Lopez-Alt fingers moisture as a key ingredient of food decay, sets the scientific method on high, and flame broils the popular Internet myth that a McDonald’s hamburger will never rot:
The final two burgers I tested were a McDonald’s burger and a regular homemade burger of the same dimensions placed in plastic zipper-lock bags side by side. Hopefully the bag would trap in enough moisture. The question: Would they rot?
Indeed they do. Within a week, both burgers were nearly covered in little white spots of mold, eventually turning into the green and black spotted beast you see above.
Read J. Kenji’s full article for more of the occasionally-moldy details – including experimental moisture measurements and graphs!