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[Photographs: J. Kenji Lopez-Alt]

A few weeks back, I started an experiment designed to prove or disprove whether or not the magic, non-decomposing McDonald's hamburgers that have been making their way around the internet are indeed worthy of disgust or even interest.

By way of introduction, allow myself to quote myself. This is from my previous article:

Back in 2008, Karen Hanrahan, of the blog Best of Mother Earth posted a picture of a hamburger that she uses as a prop for a class she teaches on how to help parents keep their children away from junk food... The hamburger she's been using as a prop is the same plain McDonald's hamburger she's been using for what's now going on 14 years. It looks pretty much identical to how it did the day she bought it, and she's not had to use any means of preservation. The burger travels with her, and sits at room temperature.

Now Karen is neither the first nor last to document this very same phenomenon. Artist Sally Davies photographs her 137 day-old hamburger every day for her Happy Meal Art Project. Nonna Joann has chosen to store her happy meal for a year on her blog rather than feed it to her kids. Dozens of other examples exist, and most of them come to the same conclusion: McDonald's hamburgers don't rot.

The problem with coming to that conclusion, of course, is that if you are a believer in science (and I certainly hope you are!), in order to make a conclusion, you must first start with a few observable premises as a starting point with which you form a theorem, followed by a reasonably rigorous experiment with controls built in place to verify the validity of that theorem.

Thus far, I haven't located a single source that treats this McDonald's hamburger phenomenon in this fashion. Instead, most rely on speculation, specious reasoning, and downright obtuseness to arrive at the conclusion that a McDonald's burger "is a chemical food[, with] absolutely no nutrition."

As I said before, that kind of conclusion is both sensationalistic and specious, and has no place in any of the respectable academic circles which A Hamburger Today would like to consider itself an upstanding member of.

The Theory Behind the Burger

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Things we know so far:

  1. A plain McDonald's Hamburger, when left out in the open air, does not mold or decompose.
  2. In order for mold to grow, a few things need to be present: mold spores, air, moisture, and a reasonably hospitable climate

Given those two facts, there are a number of theories as to why a McDonald's burger might not rot:

  1. There is some kind of chemical preservative in the beef and/or bun and/or the wrapping that is not found in a normal burger and/or bun that creates an inhospitable environment for mold to grow.
  2. The high salt level of a McDonald's burger is preventing the burger from rotting.
  3. The small size of a McDonald's hamburger is allowing it to dehydrate fast enough that there is not enough moisture present for mold to grow
  4. There are no mold spores present on McDonald's hamburgers, nor in the air in and around where the burgers were stored.
  5. There is no air in the the environment where the McDonald's hamburgers were stored

Of these theories, we can immediately eliminate 5, for reasons too obvious to enumerate. As for number 4, it's probably true that there are no live molds on a hamburger when you first receive it, as they are cooked on an extremely hot griddle from both sides to an internal temperature of at least 165°F—hot enough to destroy any mold. But in the air where they were stored? Most likely there's mold present. There's mold everywhere.

Theory 1 is the one most often concluded in the various blogs out there, but there doesn't seem to be strong evidence one way or the other. If we are to believe packaging and nutrition labeling (and I see no reason not to), there are preservatives in a McDonald's bun, but no more than in your average loaf of bread from the supermarket. A regular loaf of supermarket bread certainly rots, so why not the McD's? Their beef is also (according to them) 100% ground beef, so nothing funny going on there, is there?

In order for any test to be considered valid, you need to include a control. Something in which you already know whether or not the variable being tested is present.

In the case of these burgers, that means testing a McDonald's burger against a burger that is absolutely known not to contain anything but beef. The only way to do this, of course, is to cook it myself from natural beef ground at home.

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I decided to design a series of tests in order to ascertain the likeliness of each one of these separate scenarios (with the exception of the no-air theory, which frankly, doesn't hold wind—get it?). Here's what I had in mind:

  • Sample 1: A plain McDonald's hamburger stored on a plate in the open air outside of its wrapper.
  • Sample 2: A plain burger made from home-ground fresh all-natural chuck of the exact dimensions as the McDonald's burger, on a standard store-bought toasted bun.
  • Sample 3: A plain burger with a home-ground patty, but a McDonald's bun.
  • Sample 4: A plain burger with a McDonald's patty on a store-bought bun.*
  • Sample 5: A plain McDonald's burger stored in its original packaging.
  • Sample 6: A plain McDonald's burger made without any salt, stored in the open air.
  • Sample 7: A plain McDonald's Quarter Pounder, stored in the open air.
  • Sample 8: A homemade burger the exact dimension of a McDonald's Quarter Pounder.
  • Sample 9:A plain McDonald's Angus Third Pounder, stored in the open air

*To read about the fascinating manner in which I procured these plain patties, please refer to the original post.

You may notice that my protocols have been slightly expanded since I first laid them out to you a few weeks ago. That's due to several good ideas in the comments section which I incorporated into my testing the day after the initial publication.

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Every day, I monitored the progress of the burgers, weighing each one, and carefully checking for spots of mold growth or other indications of decay. The burgers were left in the open air, but handled only with clean kitchen tools or through clean plastic bags (no direct contact with my hands until the last day).

At this point, it's been 25 days, 23 calm, cool, and collected discussions with my wife about whether that smell in the apartment is coming from the burgers or from the dog, and 16 nights spent sleeping on the couch in the aftermath of those calm, cool, and collected discussions. Asides from my mother, my wife is the fiercest discusser I know.

Frankly, I'm glad this damn experiment is over. On to the results.

The Results

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Well, well, well. Turns out that not only did the regular McDonald's burgers not rot, but the home-ground burgers did not rot either. Samples one through five had shrunk a bit (especially the beef patties), but they showed no signs of decomposition. What does this mean?

It means that there's nothing that strange about a McDonald's burger not rotting. Any burger of the same shape will act the same way. The real question is, why?

Well, here's another piece of evidence: Burger number 6, made with no salt, did not rot either, indicating that the salt level has nothing to do with it.

And then we get to the burgers that did show some signs of decay.

Take a look at both the homemade and the McDonald's Quarter Pounder patties:

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Very interesting indeed. Sure, there's a slight difference in the actual amount of mold grown, and the homemade patty on the right seems to have shrunk more than the actual Quarter Pounder on the left (I blame that mostly on the way the patties were formed), but on the whole, the results are remarkably similar. That a Quarter Pounder grows mold but a regular-sized McDonald's burger doesn't is some pretty strong evidence in support of Theory 3 from above. Because of the larger size of a Quarter Pounder, it simply takes longer to dehydrate, giving mold more of a chance to grow.

We can prove this by examining the weight charts between the regular burger and the Quarter Pounder. Take a look:

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This chart represents the amount of weight lost from the burgers through evaporation every day (both starting weights have been normalized to 1). As you can see, by the end of 2 weeks, both the regular burgers and the Quarter Pounders ended up losing about 31% of their total weight and are pretty much stable. They are essentially burger-jerky. A completely dehydrated product that will never rot, as without moisture, nothing can survive.

Now the interesting part of the charts is during the first 4 days. As you can see, the blue line representing the regular burger dips down much more precipitously than the red line representing the Quarter Pounder. In fact, 93% of the moisture loss in a regular burger occurs within the first three days, which means that unless mold gets a chance to grow within that time frame, it's pretty much never going to grow.

The Quarter Pounder, on the other hand, takes a full 7 days to dehydrate to the same degree. It's during this extra three day period that the mold growth began to appear (and of course, once the burger had dehydrated sufficiently, the mold growth stopped—the burger looked the same on day 14 as they did on day 7). For the record, the Angus Third Pounder also showed a similar degree of mold growth in the same time frame.

So Can It Mold?

So we've pretty much cleared up all of the confusion, but a keen scientist will notice that one question remains to be answered. We've proven that neither a McDonald's burger nor a regular home-made burger will rot given certain specific conditions, but are there conditions we can create that will cause it to rot, and more importantly, will the McDonald's burger rot as fast as the homemade burger?

The final two burgers I tested were a McDonald's burger and a regular homemade burger of the same dimensions placed in plastic zipper-lock bags side by side. Hopefully the bag would trap in enough moisture. The question: Would they rot?

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Indeed they do. Within a week, both burgers were nearly covered in little white spots of mold, eventually turning into the green and black spotted beast you see above.

The Conclusion

So there we have it! Pretty strong evidence in favor of Theory 3: the burger doesn't rot because it's small size and relatively large surface area help it to lose moisture very fast. Without moisture, there's no mold or bacterial growth. Of course, that the meat is pretty much sterile to begin with due to the high cooking temperature helps things along as well. It's not really surprising. Humans have known about this phenomenon for thousands of years. After all, how do you think beef jerky is made?

Now don't get me wrong—I don't have a dog in this fight either way. I really couldn't care less whether or not the McDonald's burger rotted or didn't. I don't often eat their burgers, and will continue to not often eat their burgers. My problem is not with McDonald's. My problem is with bad science.

For all of you McDonald's haters out there: Don't worry. There are still plenty of reasons to dislike the company! But for now, I hope you'll have it my way and put aside your beef with their beef.

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