A woman who left a cheeseburger in her wardrobe as an experiment then forgot about it has found it five years later. Somewhat distressingly, it looked pretty much exactly the same as when it was first served up to her in McDonald's.

Megan Condry, from Washington DC, told NY Post that she was sorting out her Christmas decorations when she knocked over a box, and a disturbingly-fresh cheeseburger fell out. She described the burger as scentless, and looking "the same as the day I bought it". However, there were a few notable differences.

“It was rock hard, as hard as a hockey puck," she said. "I could probably smash a window with it."

Condry is not the first to conduct such an experiment. Many others have noticed that McDonald's burgers – though you would surely be in for some intense gastrointestinal distress and/or some light death should you actually consume a very old burger – don't appear on the outside to age all that much when stored in certain conditions.

McDonald's is aware of the rumor and has responded to them, vehemently denying that their food will never rot. 

"In the right environment, our burgers, like most other foods, could decompose," they explain in a blog post on the topic. "But, in order to decompose, you need certain conditions – specifically moisture. Without sufficient moisture – either in the food itself or the environment – bacteria and mold may not grow and therefore, decomposition is unlikely."

"Look closely, the burgers you are seeing are likely dried out and dehydrated, and by no means 'the same as the day they were purchased.'"

This explanation has some backup. J. Kenji López-Alt, chef and culinary consultant of the blog Serious Eats, performed a series of experiments to get to the bottom of why McDonald's burgers refuse to die like other burgers. After ruling out preservatives by looking at the patty and bun contents, he tested McDonald's burgers as well as other burgers cooked to the same shape and size, before storing them for long periods.

"The reason a McDonald's burger doesn't rot has nothing to do with chemicals, lack of nutrition, or anything else you should be scared of. It all comes down to water activity," he wrote in a blog post on the topic.

"See, a McDonald's hamburger is small and thin, giving it a very high ratio of surface area to volume. It is cooked well-done on a very hot griddle. These factors contribute to rapid moisture loss, resulting in a burger that dries out long before it can start to rot.

Moreover, the burgers are cooked in a food-safe environment to a very high temperature that kills any bacteria, and are thus relatively free of any agents of decay to begin with."

He goes on to say that McDonald's burgers without this high surface area – or burgers that are stored in moist environments – decomposed in a way we find more typical. Meanwhile, he found that burgers the same size and shape as McDonald's burgers were preserved in the same way as McDonald's.