Pictures of McDonald’s burgers that have been sitting around for years with no visible sign of decay, like the 7-year old one at left, have shocked and delighted the internets, but what’s the science behind the madness? Is it because McDonald’s is a lab experiment that we collectively hallucinate as being actual food? Salon asked the experts to find out.

Overall, McDonald’s products are both low in moisture and highly resistant to moisture. Without the dew, mold doesn’t have room to grow. More specifically:

* High fat content: equals low moisture
* Thin fries and patties: increased heat per surface area, killing more bacteria and moisture
* Coated and/or filled with salt: draws out moisture. Bacteria can’t survive without liquid

Salon writes, “A Happy Meal manages to stay unspoiled because it is fatty, salty and practically empty of nutrients — which, really, are all good reasons to avoid it anyway.”

The secret to the immortality of McDonald’s food [Salon]

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