Why McDonald's Hamburgers Don't Rot

Are McDonald’s* hamburgers immune to natural processes like rotting? There’s some evidence that they are, but a truly scientific inquiry into the matter has been lacking – until now. J. Kenji Lopez-Alt of Serious Eats tested nine different hamburgers of varying sizes (both homemade and from McDonald’s) to find out. Contrary to popular belief, the non-rotting phenomenon isn’t due to the mysterious chemical composition of the burgers. “[T]he burger doesn’t rot because its small size and relatively large surface area help it to lose moisture very fast,” writes Lopez-Alt. “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?” (HT: Chris Blattman) *Interestingly, the McDonald’s website doesn’t use the word “McDonald’s” at all except in its copyright tag; the golden M does all the work. [%comments]

David Chowes, New York City

The burgers I make at home are about 6 oz. McBurgers are 1 oz. each. Ergo, the McSmall version (I believe) has 1/6 the capacity to rot.

As far as the BigMac goes -- well, I can't comment without a
scrupulous scientific study.

Generally when burgers are very much cooked... The limit is burnt ash -- which, of course is just carbon and that does not have the posibility of rotting. My home made burgers are as rare as they can be -- close to raw. A far more potential rotten conundrum.

The McArch logo does impress me -- other companies would die for such branding recognition.

Now that we've setteled this important issue... On to nuclear proliferation, global warming, world peace...

Drill-Baby-Drill Drill Team

A science teacher in Maine has a 12 year old unwrapped Hostess Twinkie that is not growing mold, spoiling or rotting. The Twinkie will graduate high school in a few years and pretty soon head to college.

Preservatives may preserve food, and maybe even your body.

Eat more Twinkies, it is the secret of eternal youth!

Arvin Bautista

I'm all for companies being transparent and all, but I always thought it was kinda silly that McDonald's would respond immediately to the first accusations, especially by saying "our burgers do TOO rot!" It seemed so childish and defensive.


What about the bun? Any bun or roll I've had at home becomes mold city after a week or two unless its in the freezer. What fungicides are in that bun?

Mike K.

Anti-McDonald's campaigners always use the hamburger for this stunt. Because a quarter-pounder, being larger and slower to dry out, would show some rot.


I was on vacation when the results were published and missed it. Thanks! Kenji writes amazing articles.

Eric M. Jones

Upon the urgings of a whining 5-year old, I just had lunch at McD's. I had the Caesar salad with grilled chicken.

Really, really good.

And the 5-year old liked the Happy Meal.


A banana fell behind my refrigerator and was there for what I am guessing was 12-14 months before I found it when doing move-out cleaning. The banana had shrunk considerably and was hard as a tree branch, but showed no signs of rot or mold. Food sometimes just dries out before it can do either, especially in low-humidity climates.

It's very trendy these days to demonize McDonald's, but take a look in your fridge. How old is that ketchup, mayo, or soy sauce? How old is the stuff in your pantry (shortening, flour, pancake syrup)? People get used to the idea of buying packaged food at the grocery store with the expectation that they can still eat it a year or two later, but criticize companies for using preservatives. At least nobody was claiming that those year-old hamburgers were still edible.


It may be high temperature and increased surface area, or it may be the microscopic organisms are just smarter than humans and know not to eat 'food' from that particular company. That's my guess.


"*Interestingly, the McDonald's website doesn't use the word "McDonald's" at all except in its copyright tag; the golden M does all the work. "

That may be true for the homepage, but they use "McDonald's" throughout the website.

doug m

There are a few comments along the lines of "why doesn't the bread mold, my bread always grows mold."

If you wrap your bread in plastic, or store it somewhere damp, it will mold. If you store unwrapped, it will get stale, and petrify. Once this happens, it will not grow mold.


Exactly. Where there's water, there's life--biology 101. Leave the hamburger in its golden wrapper and it'll look just like the horrifying, alien-like loaf of bread I neglected for weeks on the top of my refrigerator. Were I to have left the selfsame loaf of bread out in the open, I'd have had bread crumbs.

Drill-Baby-Drill Drill Team

doug m:

There is more to decay than mold.
Rats, Mice, Roaches, other Insects, Bacterial Colonies, Protozoans, Fungi, Flatorms, Roundworms. Parasites, Putrefecation, Water Damage, UV Damage, Heat Damage, Oxidation.

Its like a party on the potato salad and Everyone is invited!

To confine all decay to mold is like saying lighting causes ALL human deaths.

Twinkie makers have engineered their product well. Too bad GM cannot similarly engineer product longevity.

Jon Prescott

Dr. Monica Hughes, a PhD biologist, has a couple of excellent posts and videos up of a thorough, well controlled debunking on this issue. McDonald's burgers and fries definitely do rot with enough moisture present.


Monica Hughes

Thanks Jon.

Anything rots, given sufficient moisture. Compact discs will rot. Rocket fuel will rot. Oil slicks will rot.

Here are the Day 26 results of my experiment. http://sparkasynapse.blogspot.com/2010/11/of-mushrooms-molds-and-mcdonalds-day-26.html

Results for the fries, whether homemade or McD's. No water: no microbes. A little water: fungi. A lot of water: little to no fungi and lots of bacteria.

Conclusion: food pretty much rots, if given sufficient moisture, whether it comes from McDonald's or anywhere else.

The inhibition of various species of microbes at certain levels of water activity (a measure of the vapor pressure of water in the food and the immediate environment) is something the food industry has known for a long time:


Maja Broz

I hope you had a nice Thanksgiving.
Do you remember how I was going to have a visual aid with that McDonald's happy meal burger? Well, I found this article in New York Times and now I am not sure if I should do it.
There is a similar version of the test with just the fries, though.
So I am wondering if the burger is a good choice.

Thank you.



Have you done the project your self? i'm doing a science project and would like some help. My family and i are organic, i did this project last year but they all rotted (I think because i put them in sealed plastic bags which yhold in the moisture.). I would like to give it another shot.

Any help??


I think I can tell the difference between a dry cured meat and a burger . And what about the bun? In more traditional countries where you can still buy real bread. I will not last till the next day with out going stale.

An example of the ingredients you would need to make bread:

Teaspoon salt
Teaspoon sugar

Ingredients of a McDonalds burger bun:

Enriched flour (bleached wheat flour, malted barley flour, niacin, reduced iron, thiamin mononitrate, riboflavin, folic acid, enzymes), water, high fructose corn syrup, sugar, yeast, soybean oil and/or partially hydrogenated soybean oil, contains 2% or less of the following: salt, calcium sulfate, calcium carbonate, wheat gluten, ammonium sulfate, ammonium chloride, dough conditioners (sodium stearoyl lactylate, datem, ascorbic acid, azodicarbonamide, mono- and diglycerides, ethoxylated monoglycerides, monocalcium phosphate, enzymes, guar gum, calcium peroxide, soy flour), calcium propionate and sodium propionate (preservatives), soy lecithin.

It really is only food for thought.



Anyone who's ever tried re-heating a Big Mac by putting into the microwave could relate to this.