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What's The Secret To Pouring Ketchup? Know Your Physics

We Americans are a nation of condiment lovers, with a special place in our stomachs for ketchup. Ranking second only to mayonnaise as the most popular condiment, ketchup is an $800 million industry in the U.S. Each American, on average, consumes a whopping 71 pounds annually.

In the 138 years that Heinz ketchup has been around, the recipe hasn't changed much. Its packaging, however, has gone through a bit of evolution, beginning with the classic glass bottles from the late 1800s. When the company introduced a more convenient plastic squeeze bottle in 1983, ketchup sales went up by 3.7 percent from the prior year. And 20 years later, Heinz revolutionized the industry with its upside-down bottles.

Despite decades of innovation, many restaurants today still prefer the glass bottles — perhaps because the iconic design reassures diners that they're getting the reigning brand of ketchup. But in all those years, it seems that consumers still haven't figured out just how to get the right amount of ketchup from these bottles onto their fries. Either nothing comes out, or, if you shake too enthusiastically, the ketchup flows so quickly that your food is swimming in a pool of red.

So what's the secret? Some say the sweet spot to tap is the neck of the bottle, where the 57 is. Others advise you to tap the side of the bottle on your arm ever so slightly.

But perhaps most helpful is understanding how ketchup works. Part of the problem lies within the physics of the condiment itself, explains educator and writer George Zaidan in a recent TED-Ed video.

Ketchup, Zaidan says in the video, is a pretty unusual substance. It behaves both like a solid and a liquid, depending on how you shake that bottle.

That's because there are two types of fluid: Newtonian and non-Newtonian. Newtonian fluids retain their viscosity — or resistance to flow — regardless of the amount of force you put on them. Non-Newtonian fluids are what Zaidan calls "rule breakers." Their thickness and viscosity change based on how long, how hard and how fast you push.

Ketchup — made of particles from pulverized tomatoes, along with water, vinegar, corn syrup and spices — belongs to the latter group and gets thinner the harder you push. Zaidan explains that below a certain point of force, ketchup behaves like a solid, leaving you frustrated with anticipation. (Carly Simon's "Anticipation," by the way, was the theme song in Heinz's late 1970s television ads.)

Once you shake the bottle beyond that breaking point, the ketchup becomes 1,000 times thinner, giving you that shower of tomato paste that drowns your fries. How? Well, when you give that bottle a good, hard shake, all those spherical particles get squished into ellipses that easily flow past each other.

But what if you're cautious like me and prefer to gently shake the ketchup out of its confinement? It will flow eventually, but scientists aren't exactly sure how. It could be that the particles form small clusters, leaving more space in between to flow past one another. Or, perhaps the particles gather at the center of the bottle, away from the walls, leaving the watery soup as a lubricant.

Zaidan says the ketchup-pouring pros know exactly how to control that flow: Keep the lid on and give the bottle a few good hard shakes to "wake up" the particles. Then, uncap and pour to your heart's content.

Of course, one could argue that it would be a lot easier to just do away with glass bottles altogether and take advantage of ketchup's squeeze bottles. But even they've left room for innovation. In early April, two high school students from Kansas City, Mo., wowed the nation with their mushroom-shaped cap invention. Its purpose? To prevent that dreaded watery ketchup soup from squirting out ahead of the good stuff.

Copyright 2021 NPR. To see more, visit https://www.npr.org.

Linda Poon