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Can Microwaves Superheat Water?

Microwaves are fantastic modern tools – although, having been first sold in 1946, developed based on technology developed in WW2, they’re actually not so modern!

They let us heat and reheat foods and drinks in a fraction of the time that traditional cooking methods do. They’ve become a useful method of convenient cooking, and for many people are an essential component of modern life.

They can save us so much time in the kitchen!

Can Microwaves Superheat Water

When heating drinks in the microwave, there is a risk of something called superheating. But what is superheating, and what sort of danger can it pose?

Can a simple mug of water be made dangerous by a microwave? This article will teach you what you need to know about microwaves and the dangers of superheating – and how you can prevent it! Read on to find out more!

What Is Superheating?

Superheating is also called boiling retardation, or boiling delay – which might go some way to explaining the phenomenon!

A superheated liquid is one that is heated beyond its normal boiling point, without actually boiling. But what does that actually mean – and how does it work in practice?

Well, the boiling point of a liquid is the temperature point at which the liquid changes into a vapor, because the pressure surrounding the liquid has equaled the vapor pressure of the liquid itself.

The term “vapor pressure” seems a little complex – what it means is really the tendency of the liquid to evaporate into a gas.

So, when a liquid boils, its vapor pressure is equal to the pressure of the air surrounding it – therefore, it turns into steam!

When a liquid is superheated, it means that it’s at the temperature where it would normally boil – and yet, it isn’t boiling! We know that water, when boiling, likes to move about a lot.

Bubbles form rapidly, pushing their way to the surface, all the time agitating and moving the water about – in addition convection, which also causes the liquid to move.

Hotter water wants to rise to the top of the kettle – and, once there, it cools more quickly than water that’s nearer to the heating element, which then moves to the top of the kettle, and so on.

A superheated liquid is extremely hot, and yet appears to be as still as a cold liquid. The temperature can be higher than the normal boiling point of the liquid, and yet the liquid hasn’t become a gas yet.

For instance, superheated water doesn’t roll and bubble in the same way that boiling water does – and yet, can be at a higher temperature!



Superheated water can be extremely dangerous! Despite looking as lacking in energy as cold water, it’s actually packed full of energy from being heated, and it’s just waiting to let off that energy as fast as possible!

Normally, water bubbles when boiled. These bubbles, which are steam – which comes from the act of heating the water – need somewhere to form.

They form on imperfections in the container, called nucleation sites. These nucleation sites can be tiny!

The bubbles expand as they rise to the surface of the water. Without these nucleation sites, a bubble can’t form – until the water is disturbed.

Once the water is disturbed, however, superheated water will form a bubble EXTREMELY quickly. So quickly, in fact, that it seems to explode!

All it takes is a spoon being put into the water, or some sugar – or even just moving the container that’s holding the water.

So, simply taking some superheated water out of the microwave can cause it to explode in your face! This is obviously extremely bad – it can cause horrendous injuries!

This is far more likely to happen in microwaves than in a kettle,in part because of how smooth containers used in a microwave can often be.

With no minor imperfections to act as nucleation sites, there’s no way for bubbles to form when the water is being heated.

But once a bubble does form, from something as simple as taking the water out of the microwave – disaster can ensue!

The burns that you can get from superheated water exploding can be extremely painful and traumatic. It can cover your head and arms in an instant, scalding you, and potentially causing serious damage.

How To Prevent It

With this danger in mind, it’s extremely important to take any steps necessary to ensure that it never happens to you! You absolutely never want to have this happen.

The first, and most simple way to prevent liquids becoming superheated in a microwave, is to never use the microwave to heat liquids!

Now, depending on your circumstances, this may be either easy, or completely unfeasible. What can you do to keep safe if you absolutely have to use a microwave to heat liquids?

Well, you may remember that to boil, a liquid must be able to bubble. And also that these bubbles need places to form, called nucleation sites.

Well, the best way to make sure that a liquid superheats is to ensure that there are nucleation sites, so that bubbles can form, and the liquid can boil normally!

You can ensure this by placing something non metallic in the container – remember, it’s generally a pretty bad idea to put metal in the microwave.

For instance, if you’re microwaving a mug of water, there’s a very good chance that the water could superheat and become extremely dangerous!

Especially if the mug is brand new, and hasn’t had time to have any minor scratches form inside. In which case, the best way to stop water superheating in it is to place something like a wooden coffee stirrer in the liquid.

Also – and this is crucial – let the liquid cool before even thinking about moving it! Just leave it in the microwave for a few minutes before even opening the microwave door.

After all, the slightest disturbance can make a superheated liquid explode – so don’t take the chance.

Even with a wooden stirrer inside to enable bubbles to form, it’s still much safer to wait a little, rather than reaching straight for the container the second you hear the microwave go ping!


Superheated water from a microwave is a very real danger – but fortunately, it’s one that you can prevent! A bit of preparation, and a bit of planning, and you’ll be much safer!

Jess Smith