REUTERS/Molly Riley

The indestructible McDonald’s burger is an Internet fad that recycles every few years. But why won’t the thing decompose?

Experiments like the Happy Meal Project show McDonald’s burgers and fries maintaining their original condition after hundreds of days. The knee-jerk reaction is to assume McDonald’s pumps mass quantities of preservatives into its food, but the truth may not be so scandalous.

Salon did some digging into this trend, and found that the fat, not the chemicals, causes the food to stay pristine. High fat means low moisture, which lends to less space for mold to grow. And since this is fast food, both the fries and the meat patty are very high in fat. The bun, however, remains a mystery — its contents are nearly identical to a loaf of Wonder bread, yet it doesn’t get moldy.