The physics of ketchup

Ainissa Ramirez is a scientist, author, and self-proclaimed science evangelist. She’s calling for big changes in science education, and as the creator of a science podcast series called “science underground.” She discusses one of her latest podcast episodes called “helping ketchup hurry up.”


Ainissa Ramirez is a scientist, author, and self-proclaimed science evangelist.

She's calling for big changes in science education and is a creator of a podcast series called 'Science Underground.'

Here to discuss one of her latest podcast episodes, called 'Helping Ketchup Hurry Up,' is Ainissa Ramirez.


So, yeah.

The science of ketchup.


[ Laughs ]

It takes so long to come out of the bottle, right?

I mean, they've even had songs, like 'Anticipation.'

Why does it take so long?

Well, if we understand what makes up the ketchup, we'll know why.

Ketchup is made of vinegar, sugar, spices, and pulverized tomato pieces.

And they can't get past each other, so they need help.

And the way that we can help it is the first thing we can do is we can shake it up.

Right. Everybody does that.

Everybody does that, but the other thing we can do is that we can force it.

So if we get the ketchup, put it at 45 degrees, and use our hand and do this chopping form, comes right out.

I've always heard -- hit at a 45 on the 57.

On the 57 -- That's right.

And the reason why we do that, the science behind it is because ketchup is what they call a yield stress thixotropic fluid.

Wow, that sounds so nerdy.

[ Laughs ] And all that means is that yield stress means that it needs a force in order for it to move.

And the thixotropic means that it has a memory.

The particles are arranged in a random way.

And if someone uses it and another person uses it, it will be easier for the second person, because they're no longer in that random structure.

They kind of are able to flow past each other, like a school of fish.

So, really, they did do the work for you.

They did do the work for you.

[ Laughs ]

Always be the second person when you get the ketchup bottle, and it will flow right out.

What are other fluids like this?

So, thixotropic materials are kind of rare.

Like, the ink inside of a space pen is thixotropic.

It's solid, and then it's a fluid.

But yield stress materials -- Mayonnaise is a yield stress material.

If you get mayonnaise and you scoop it out, you put it in the refrigerator, you come back, that scoop is still there.

If it were a liquid, like honey, it would flow, it would recover.

You would never see that divot.

But mayonnaise, you see that scoop, and it'll stay there for a long time.

So there are other materials -- and blood is also a yield stress material.

How do they think about this kind of effect and this kind of -- just, really, the science behind this when you think about medical research or when you think about any kind of scientific research?

Well, actually, it's still very much an open question about how ketchup behaves.

There are a lot of mathematicians still working on it -- how the particles, the tomato particles, are being moved.

But if they can figure it out, it gives us a better way to process foods -- like, large-scale vats of foods.

How do we make sure that it moves through nozzles in a uniform way?

Also, it could be used to control if we have an oil spill.

If we have special, smart liquids that can thicken in certain ways, we can control where these spills go.

So that's why scientists are working on these crazy yield stress thixotropic materials.

What's happening on a granular level?

I mean, if we took a microscope or even something more powerful, how would we see all these chunks of tomato and vinegar and whatever else -- the special 57 ingredients in there?

[ Both laugh ]

57 varieties.

Well, the tomato pieces are randomly arranged.

They're all over the place.

And if I -- When I shake it, the tomato pieces elongate a little bit, but then they also form this kind of channel, if you will, where they all kind of are in one direction.

So when I turn it over and hit them, then they all can go in this place where it's easier for them to flow.

So, the tomato pieces are randomly arranged, and then by moving it, by shaking it, we give them some kind of order.

And that helps it moving -- to move out of the bottle.

And I'm assuming the difference between this and one of those red things that you see in every restaurant is that there's air pressure inside, and when we squeeze, shove it out.

The reason why it's hard to get a glass bottle of ketchup is that people -- They hardly manufacture these things.

You can only see them in restaurants.

It's because when they switched to the squeeze bottles, the sale of ketchup went up tremendously, 'cause people are really sick of waiting for ketchup to come out.

But when you squeeze it, you can totally control how it comes out.

All right, Ainissa Ramirez.

The science of ketchup explained.

Thank you.