The Skinny on Big Beef: Why Fast Food Burgers Don't Seem to Rot

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by Nicole Kobie

McDonald's burgers are famous for not rotting. But is there something really unique (or terrible) about their version that makes the menu item indestructible? Not particularly.

One of the most famous cases of a well-preserved fast food lunch is still being displayed in Iceland today. McDonald's closed its last restaurant there in October 2009, as the country was engulfed in economic disarray. Local Hjörtur Smárason bought a cheeseburger on the restaurant's last day, but rather than eating his lunch, he tucked it away. He kept it on a shelf in his garage to see what happened, having heard the rumors that McDonald's burgers don't decay. There it sat until 2015, when Smárason donated it to Iceland's national museum. Eventually, it found a new home, on display at the Bus Hostel Reykjavik.

And you don't need to visit Iceland's capital to see the notorious meal. The hostel has set a webcam on the disturbingly fresh looking burger, so we can all watch it rot and decay. But as the hostel notes: “You might have to be patient though to see any changes.”

They're not wrong. There's a proud tradition of ancient McDonald's burgers being displayed to the world rot-free. Utah resident David Whipple has held onto one such hamburger since 1999, after finding it in his jacket pocket a year after buying, along with the receipt. Though it doesn't look tasty, it still looks like a burger. The pickle has disintegrated, but, according to Whipple, there was no decomposition or mold on the meat or the bun.

Artist Sally Davies bought a Big Mac in 2010 and has photographed it every day since, dubbing it the "Happy Meal Project." Even on March 5, 2017, the 2622th day, her photos reveal the Big Mac meal hasn't changed its looks. However, she did report that the meat and fries had turned to a “very hard material that feels similar to plastic.” She also offered the aging food to her two dogs, but they “were not interested.”

But burgers from the Golden Arches aren't that special, at least according to the company. McDonald’s has been asked on its own FAQ pages why its food doesn't rot.

"In the right environment, our burgers, fries and other menu items could decompose," the response read, adding that, "The reason our food may appear not to decompose comes down to a matter of simple science. In order for decomposition to occur, 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. So if food is or becomes dry enough, it is unlikely to grow mold or bacteria or decompose. Food prepared at home that is left to dehydrate could see similar results."

Not convinced? To back up that explanation, McDonald's also found Dr. Keith Warriner, program director of the University of Guelph's Department of Food Science and Quality Assurance. “The reality is that McDonald’s hamburgers, french fries and chicken are like all foods, and do rot if kept under certain conditions,” he is quoted by the fast food restaurant chain as saying, pointing out that without water, nutrients, and warmth, food won't spoil.

While most of the ancient-burger blogs suggest the lack of spoilage is down to McDonald's food being short on nutrients, Dr. Warriner said it's actually a lack of moisture, pointing out that the meat patty loses water during cooking and the bun is toasted. He suggested that wrapping a burger in cling film or leaving it in a damp place would cause it to rot.

Others have tested that theory. J Kenji Lopez-Alt at Serious Eats's Burger Lab took a more scientific approach to watching old McDonald's burgers, testing nine hamburgers from multiple sources under different conditions.

After a month, the more stringent test run by Lopez-Alt revealed that none of the regular-sized burgers rotted if left in the open air, whether they were from McDonald's or not. However, larger sized patties—homemade or the McDonald's Quarter Pounder—both developed mold. Lopez-Alt suggested that's because the smaller size of the regular burgers let them dehydrate more quickly, avoiding mold, with weight tests throughout the month appearing to support that.

A further test, in which a regular burger and a similar-sized homemade one were both kept in plastic bags, also backed up McDonald's claim that lack of moisture staves off mold and rot. Both burgers showed signs of mold within a week.

In other words, if you wrap it up tight, your burger will rot within a week; if you let it dry out, it'll last years. Either way, buy a fresh one if you're hungry.