The real reason why fast food burgers don’t rot

Fast food has been associated with a poor diet for the last few decades, but few visuals really drive home how unnatural these items are in a diet like the notorious non-rotting McDonald’s burger.

If you aren’t familiar with the original story, in 1996, a woman by the name of Karen Hanrahan bought a burger from McDonald’s. She has since maintained a blog about the burger–which has remained unchanged since the day she bought it. Other burgers, like those prepared at home, would have long since rotted away, suggesting that there was something unwholesome in the fast food burger that prevented even bacteria or mold from wanting to consume it.

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The results were replicated recently in a Buzzfeed video showing seven burgers from seven different fast food chains. The burgers were stored in glass jars for 30 days, and at the end of that 30 day period, some had mold while other–the McDonald’s sample included–did not look any different from the day they had been purchased.

This latest video has once again stirred up the controversy surrounding fast food burgers, striking fear into the hearts of people regarding chemicals in food and processed meat. The truth behind the mystery, however, may be far less sinister and likely has no impact on human health whatsoever.

When the original Hanrahan burger was making its rounds, renowned chef and food blogger J. Kenji López-Alt took it upon himself to conduct a small investigation into why the MCDonald’s burger didn’t mold like a burger cooked at home. He theorized in his blog Serious Eats the following possibilities for the phenomenon:

• There was something in the beef that’s kept the burgers from rotting.
• There was something in the bun that’s kept the burgers from rotting.
•  There was some sort of magical alchemic reaction that kept the burgers from rotting only when a McDonald’s patty came in contact with a McDonald’s bun.
• The size of the patties prevent the burger from rotting.
• The storage environment prevents the burgers from rotting.

Ultimately, López-Alt needed to determine what prevented the burgers from molding, so he needed to look at what mechanisms inhibit mold growth. Expanding on his above determinations, he narrowed the investigation down to: presence of some special preservative in the meat or bun, high salt content in the burger, low moisture content, no mold spores ever coming into contact with the burger, or no air where the burger was prepared.

He then purchased McDonald’s burgers and prepared burgers of his own, prepared in the same dimensions as a burger from the fast food restaurant. All in all, he prepared 9 different case studies; some burgers had extra salt, some McDonald’s burgers were pair with store-bought buns, and so on.

At the end of his 3-week study, the McDonald’s burger hadn’t molded–but neither had the no-additives, homemade patty he prepared with the same dimensions.

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The conclusion? Of all the theories tested, it appeared that moisture content was what ultimately preserved the two burgers. Due to how thin the patties were and how much surface area they had, both the homemade burger and the McDonald’s burger had lost 25 percent of their weight within the first week, indicating they had dried out. The Environmental Protection Agency (EPA) clearly states mold needs moisture to grow, and even though mold spores are present almost everywhere, they will not cause something to decompose unless moisture is present. This is why bread, when left out in the open air, goes stale and becomes hard and bread left in a bag molds due to higher moisture content.

So, rest assured that when fears about the non-rotting McDonald’s burger flare up as they tend to do every few years, it’s not from a process of harsh chemicals or food additives. The preserved burgers are simply nature being nature. That doesn’t mean you should still consume the burger after it has been left out, and it doesn’t mean that fast food is any better for your diet. What it does mean is that you should always question information that seems to defy the laws of science; there’s usually a good explanation for everything.