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Why McDonald's Burgers Don't Rot: It's Not What You Think

It is well known that McDonald's burgers can sit out for years without showing signs of decomposition.

This ominous phenomenon is well documented, and a quick Google search will show countless old burgers, even one from 1996, Business Insider reports.

One Nebraska chiropractor's office proudly displays a nearly intact McDonald's Happy Meal that is a few years old in an attempt to keep patients away from fast food:

Dan Whipple of Utah has a burger from 1999 that still has not rotted:

Whipple originally forgot about the burger for a couple years and found intact. He now reportedly shows it to his grandchildren to impress upon them just how many chemicals and preservatives are in fast food.

But according to McDonald's Canada, the burgers "do rot under certain conditions," Dr. Keith Warriner wrote on the franchise's official website.

Essentially, the microbes that cause rotting are a lot like ourselves, in that they need water, nutrients, warmth and time to grow. If we take one or more of these elements away, then microbes cannot grow or spoil food.

In the example of a McDonald’s hamburger, the patty loses water in the form of steam during the cooking process. The bun, of course, is made out of bread. Toasting it reduces the amount of moisture. This means that after preparation, the hamburger is fairly dry. When left out open in the room, there is further water loss as the humidity within most buildings is around 40%. So in the absence of moisture or high humidity, the hamburger simply dries out, rather than rot.

Warriner went on to suggest that a similar homemade burger would not rot either.

He is right.

To test this out, food blog A Hamburger Today experimented with several kinds of McDonald's and homemade burgers. Like the McDonald's burgers, the homemade ones with similar dimensions did not rot, while a larger homemade burger and a McDonald's Quarter Pounder both did, leading AHT to conclude that the small, flat surface area of the smaller burgers allow them to completely dehydrate before mold has the opportunity to grow.