Why Does Ravioli Float When Cooked?

RavioliJohn Sphepherd via Canva.com

Why does ravioli float when cooked? I started asking myself this question as I watched ravioli cook in a gentle boil the other day. Then I fell into the rabbit hole of researching it on the Internet—and the answer turned out much more complicated and intriguing than I anticipated.

If you came here just as curious about this pasta mystery as I was, keep on reading.

Cooked ravioli floats your pasta water because of density. Frozen ravioli is denser than water, so it sinks. When ravioli cooks, its density decreases, which causes it to float.

It’s all about the physics of cooking pasta.

When the food in a pot of water is less dense than the water, it floats. Conversely, when the food is denser than the water, it sinks. 

The avg. density of water is roughly 1 gram/millimeter (or 997 kilograms/cubic meter). As the temperature of the water rises and falls, its density changes. The density of water can also change when you dissolve something, like salt or the starches from pasta noodles, in it.

Here’s the thing: it’s unlikely that ravioli floats as it cooks because it’s less dense than the pasta water

The reason is still in density, but not because the ravioli is less dense than the water. Scientists suspect that there’s probably something else in play.

Your ravioli floats in the pasta water because of something called convection currents

When you heat water in a pot, it becomes less dense and rises to the surface. And it’s replaced by the less dense water that surrounds it. 

But because the denser water is sitting closer to the hot bottom of your pot, it is in turn heated. So it becomes less dense and rises to the surface, only to get replaced again by the less dense water surrounding it.

This cycle is called convection, and the movement in the water that it creates is called a convection current. As you heat water in a pot, convection currents form as hot water continually rises to the surface and keeps getting replaced by the colder (and denser) water around it.

Source: Georgia State University (Heat Transfer)

When you take out ravioli from the freezer, they’re as dense as they can be because the cold air has caused them to go into a solid state. Put them in a pot of boiling water, and they start to rehydrated and heat up. The rise in internal temperature causes them to lose density.

The theory is that, as ravioli cooks in a pot of boiling water, it loses enough density to be lifted to the surface by the convection currents in the pot.

I haven’t measured this with any instruments, but I have thought it through after much research and geekery.

You can put this theory to the test by yourself. Just turn off the heat when you’re boiling ravioli—and the pasta will sink as soon as the convection currents in the bot slow down and fade out.

Eggs could also be helping fresh ravioli float on the surface of the pasta water as it cooks, according to Professor Dr. Christopher Brock. He teaches bakery science at London South Bank University.

“This is where the egg comes into play. It is rich in emulsifiers, which trap air inside the dough while it is being mixed and kneaded,” Prof. Brock tells The Naked Scientists

“The air remains in the cooked pasta making it more buoyant, and it’s the combined effect of the reduction in density as the starch becomes a gel and the buoyancy of the trapped air that makes the fresh pasta rise to the surface.”

Prof. Brock also goes on the explain why pasta noodles lose density as they rehydrate and cook: “When pasta is cooked and it reaches about 60 degrees C, the starch granules absorb water and swell and this causes the amylose to contact and attach to the amylose from neighboring starch granules.” 

“Imagine, if you will, the way that the wax in a lava lamp is exuded and merges with other globules of wax – it’s a similar process. Eventually, the starch is converted into a gel pervading throughout the cooked pasta. This gel contains more water and is less dense than the starch granules in raw dough.”

The Bottom Line

To sum it up, why do ravioli float when cooked?

It turns out that there are three reasons that, when combined, make ravioli float on the surface of your pasta water as they cook it in the pot:

  1. The ravioli loses density.
  2. Convection currents form in the water.
  3. The emulsifiers from the egg trap air in the dough, making it more buoyant.

Remember the physics of pasta the next time you make ravioli at home 🙂 .

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