Sally Davies's claim that McDonald's hamburgers simply don't decompose has been kicking around for six months. Over that span she observed a Happy Meal (an endangered species) in her kitchen that didn't mold, rot or shrink and she posted the pictures to prove it. Media attention piled on and, naturally, McDonald's spokespeople got very testy—heatedly insisting that, yes, their patties do actually mold. The truth, according to one kitchen scientist, is that both of these claims are suspect.

"Neither a McDonald's burger nor a regular home-made burger will rot given certain specific conditions," argues J. Kenji Lopez-Alt at Seriouseats.com, who undertook an experiment to empirically test Davies claim with a control burger and a McDonald's patty. After several weeks of tinkering (pictures, graphs and multiple hypotheses included on the site), the experimenter concluded:

Turns out that not only did the regular McDonald's burgers not rot, but the home-ground burgers did not rot either. Samples one through five had shrunk a bit (especially the beef patties), but they showed no signs of decomposition. What does this mean? It means that there's nothing that strange about a McDonald's burger not rotting. Any burger of the same shape will act the same way.
Why, you may ask, did these burgers not immediately begin to decompose?
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?
[H/T: The Morning News]