An important part of conducting an experiment is to have a control to compare it against. We can see that this particular burger doesn't seem to be rotting, but is that unusual or unexpected?
Morgan Spurlock, in the movie Super Size me conducted an experiment with a number of McDonald's burgers and burgers from other sources, placing them in glass jars.
The results were that all of the burgers were rotting after a few weeks. (Yes, they were at different rates, but larger samples sizes would be required to see if that was was significant, as well as controlling for more variables, like burger size.)
Another experiment was started here by Serious Eats.
It looked at a number of different questions:
- Whether it's something in the beef that's keeping the burgers from rotting.
- Whether it's something in the bun that's keeping the burgers from rotting.
- Whether it's some sort of magical alchemic reaction that keeps the burgers from rotting only when a McDonald's patty is in contact with a McDonald's bun.
- Whether it's the size of the patties that are preventing the burger from rotting.
- Whether it's the storage environment that is preventing the burgers from rotting.
In the conclusion, it found that burgers (McDonalds or home-made) stored in the open air, where they could dry out, had little or no mould. Burgers (McDonalds or home-made) stored in plastic bags that held in the moisture (like Spurlock's glass jars) got mouldy.
Pretty strong evidence in favor of Theory 3: 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?
So, no, McDonald's burgers do not have an unnaturally long lifespan. They have a similar lifespan to other commercial and homemade burgers. Whether they are abnormal or unhealthy is an unrelated question!
Note: Neither experiment was documented in a peer-reviewed journal; I think it will be hard to find a journal that would publish such an experiment.