Nothing says independence like eating an unnaturally pink finger of processed meat. The color of a hot dog is weird, sure, but would you have it any other way? On July 4, an estimated 150 million hot dogs will be consumed across America, and chances are your hot dog will have the disconcertingly smooth, consistently reddish-brown shade of pink that Americans have loved for over 150 years. And on a day that’s all about tradition, it’s the only way to go.

“Hot dogs are the all-American food so it’s natural that we eat them on the all-American holiday,” says Eric Mittenthal, the president of the National Hot Dog and Sausage Council, in an email to Inverse. “July 4th is a holiday best celebrated outdoors and hot dogs are a guaranteed outdoor eating crowd pleaser for all ages.”

What is also guaranteed is that the color of your hot dog is unnatural. Hot dogs are traditionally made with a mixture of mashed-up pork and beef trimmings that are swirled together with processed chicken trimmings, food starch, flavorings, corn syrup, and lots of water to give it that characteristically smooth texture.

None of those ingredients are the color of a hot dog. You could make the case for beef, if it’s just been cut from a cow, but the meat that’s going into a hot dog is far from grade A. The magic moment that a tube of meat slurry becomes a hot dog happens when the secret ingredient — sodium nitrite — is added to the mix.

There's a reason they always look so darn fresh. Flickr / yummyporky

Why Meat Is Pink In the First Place

Sodium nitrite is added to hot dogs — as well as other processed meats, like bacon, cold cuts, and Spam — to “cure” or preserve the meat, add flavor, and develop its characteristic color (bonus: it prevents the growth of botulism-causing bacteria). But the reason meat is red in the first place is because of a pigment in the muscles called myoglobin.

Like its blood-borne cousin hemoglobin, myoglobin’s job is to carry around oxygen. When myoglobin is bound to oxygen atoms, it gives off a bright red color. That color, in turn, comes from the part of the myoglobin molecule known as “heme” — a chemical structure that has an atom of iron at its core. For the same reasons that rust (an “iron oxide”) is red, myoglobin is red when its iron molecules get to hang out with oxygen.

Fresh beef is red because its myoglobin molecules are still bound to oxygen, but they can’t hold on to oxygen forever. This is why meat turns an unappetizing grey as it gets old: As oxygen atoms fall off heme’s iron ring, the iron’s changing oxidation level turns it increasingly pale. But not when sodium nitrite is around.

Myoglobin's redness comes from the heme group at its center, which contains an atom of iron that binds oxygen.

Sodium Nitrite’s Bait-and-Switch

Sodium nitrite binds heme in place of oxygen, essentially tricking the myoglobin into staying red. It stays bound much longer than oxygen would, which is why meat treated with sodium nitrite looks red so much longer than untreated meat. According to a 2011 study funded by the American Meat Science Association, only 2 to 14 parts per million (ppm) of sodium nitrite is necessary to produce the “cured color.”

We salute you, sodium nitrite! Flickr / stevendepolo

Sodium Nitrite’s Dark Side

Sodium nitrite and its cousin sodium nitrate, which serves the same function, don’t have the best reputation. Many animal studies link high doses of nitrites with a higher incidence of cancer, pointing to the fact that when meat treated with nitrites is overcooked or charred, it can form compounds called nitrosamines, some of which are carcinogenic.

But as with all compounds, the poison is in the dose. According to the US Food and Drug Administration, sodium nitrate used as a color fixative shouldn’t exceed 200 ppm in the “finished meat product” (the limit is 500 ppm for sodium nitrite). According to the European Food Safety Authority’s 2017 nitrite and nitrate guidelines, the acceptable amount of sodium nitrite to consume is between 0.06 and 0.07 milligrams per kilogram of body weight per day (for nitrate, it’s 3.7).

In 2017, Oscar Mayer debuted an “all natural” hot dog that uses celery juice, which is naturally rich in sodium nitrite, as a preservative, instead of the artificially derived compound. While it was touted as a healthier version of the classic product, experts weren’t convinced it was any healthier than regular dogs.

Hot dogs come in various shades, but they are generally described as "pink". Screenshot via Pantone

Salute Tradition

Consuming processed food regularly isn’t a great idea, but an occasional hot dog probably won’t hurt. If you do choose to celebrate America’s independence the traditional way, take a moment to appreciate the complex chemistry that makes your hot dog pink before slathering it with toppings. If you’re anything like Mittenthal, you’ll still see some of it peeking through.

“As for me…I love a good chili dog with mustard and onions but on the Fourth, I tend to keep it simple with a grilled hot dog (or two or three) with mustard and onions,” Mittenthal says.

Chili dog: more than just nitrites. Flickr / CityofStPete

This article was first published in 2018.