Putting a closed container with water on heat sounds like a bad idea. Can a moka pot explode and if so what can you do to prevent this?
In very rare situations a moka pot could explode if both the safety valve and filter are completely blocked/stuck. The safety valve and filter basket can get clogged up by deposits that build up with use over time. With proper cleaning and maintenance, these deposits can easily be prevented.
If it turns out you need a new moka pot because it still doesn’t work properly after cleaning, make sure you get one from a well-known brand so there are replacement parts available. Bialetti (Amazon) is the original moka pot brand and is still a good choice.
Let’s get a little deeper into why and how this can happen and how to prevent this from happening to you. Keep reading to find out.
Can a Moka Pot Explode?
The quick answer is; yes, a moka pot can explode under the ‘right’ circumstances.
There is boiling water in the bottom part of a moka pot. Boiling water creates steam which creates a lot of pressure. In normal situations, that pressure is used to push the water through the coffee grounds and brew coffee. When that process is interrupted (we’ll go into the specifics below), there is another safety mechanism. you might see a little bronze-colored part on the top of the moka pot boiler. This is a pressure valve. These are supposed to open and release pressure when it gets too high. For the moka pot to explode, both those ways of releasing pressure will have to be blocked or stuck.
Now explosion might sound quite scary and it can certainly be. What usually happens is that the coffee/water bursts out from the connection between the lower vessel and the coffee container. Sometimes there is a bit more serious separation of the top and bottom parts.
So there is no explosion where the metal container explodes and blows shrapnel everywhere. There are many parts of a moka pot that will fail before the actual cast aluminum container will.
However, that’s not to say the failure that can happen isn’t scary and possibly destructive. It certainly can be. Usually, it will just involve getting a lot of coffee all over your kitchen but sometimes it can cause more damage. The top blowing off a moka pot could damage your kitchen and more if it gets bad. However, this is quite rare and there are some easy ways to prevent this.
Are you not yet 100% sure how to brew good coffee with a Moka pot? Click here to find a step-by-step guide.
How Common Is a Moka Pot Exploding?
Although it’s impossible to find concrete data and numbers, it happens. There are pictures and videos on the internet that show this. However, there are also many, many people that this never happens to. There are probably millions of moka pots out there all over the world and this is not anywhere near a daily occurrence.
Many people use it every day without any problems. There are hundreds of thousands of cups of coffee being made with these things every day without any problems.
The good news is that moka pot problems don’t just happen completely at random. There are some factors that contribute to a potential explosion. When you know those you can prevent anything bad from happening so you can feel safe while making your morning coffee.
So let’s get into what causes moka pots to explode and what you can do about it.
What Can Cause a Moka Pot To Explode?
A Moka pot brews coffee with pressure. You put water in the lower vessel and heat it up. That heat creates steam. Steam takes up much more space than water so the pressure in the container rises. That pressure wants to go somewhere.
The mechanism of a moka pot is to direct that steam pressure to push the water through the bed of coffee into the collector. That’s the only way the pressure is supposed to be relieved because if that doesn’t happen, you don’t brew any coffee.
In case the steam can’t go through the coffee grounds for whatever reason, there is a pressure relief valve in the water vessel. This pressure valve is supposed to relieve the pressure if it gets too high. Pressure will find the way of least resistance. Usually, that’s through the coffee grounds and if that way is obstructed, the pressure valve is supposed to let off the pressure. A moka pot creates about 1.5 bar of pressure under normal circumstances and the valve opens when it’s significantly more than that but before structural damage can happen to the metal parts.
Where things really start going wrong is if both ways of relieving pressure are blocked/stuck. Pressure valves can get stuck over time. Most of the time you don’t notice this because the pressure is used to brew coffee. But if that way is suddenly blocked, you’ll find out in a dramatic fashion that the valve is stuck as well.
Just to be clear: Both the filter and the pressure valve have to be blocked for a really bad blowout to occur. And even then, it’s not a guarantee. There will be some signs to look for so you can stop anything really bad from happening.
There are a few reasons for the filter basket and the pressure valve to get blocked:
- Coffee ground too fine. This blocks the holes in the filter, blocking the holes means steam/liquid can’t go through, building up pressure. Alternatively, the grounds are packed so close together that water can’t get through. It’ll have to be really finely ground coffee for this to happen. The best grind size for a moka pot is slightly larger than for espresso.
- Coffee is tamped too hard. Coffee grounds shouldn’t be tamped down in a moka pot. Usually, the water will channel through the grounds if this is done which results in weak coffee but sometimes it can block the whole filter.
- Pressure valve is stuck. This can be because the minerals in your water create deposits over time, which block the movement of the valve. Possibly coffee grounds can make their way in there as well doing the same thing as water deposits. You can clean this off pretty easily.
- The pressure valve is of bad quality and doesn’t work properly in the first place: This is a risk when buying a moka pot that’s very cheap. It will be made with cheap parts. Most of the time it’ll be fine but, the parts and quality control won’t be on the same level as from a brand like Bialetti.
Those are the reasons, but what can you do to prevent this? Keep reading below to find out.
How To Prevent a Moka Pot Accident?
So, from the causes in the previous paragraphs, we can find some preventative measures that can prevent coffee accidents from happening. You wouldn’t want to waste your coffee!
By looking at the causes, we can prevent bad things from happening with your moka pot. Here’s a list of the potential problems and their solutions;
|Steam can't go through coffee grounds||Coffee ground too fine||Adjust grinder or buy different coffee|
|Coffee grounds tamped too hard||Don't tamp coffee down in moka pot filter|
|Pressure valve doesn't relieve (enough) Pressure||Pressure valve was never operational||Get a higher quality moka pot|
|Mineral deposits block valve||Regularly clean moka pot|
|Coffee grounds/deposits block valve||Regularly clean moka pot|
|Too much water in vessel||Only fill vessel up to just under pressure valve|
|Pressure valve can't relieve fast enough||Don't put moka put on high heat. Use medium heat.|
Moka pot safety tips
Besides the things listed above which directly aim to fix the causes, there are some other things you can do. Since you don’t really know if a safety valve works until you need it, some other precautions can be helpful.
- Start with hot water: This will shorten the time you need to wait before your moka pot starts sputtering. So if you don’t hear and/or see any coffee being brewed within one or two minutes, you know there is something stopping the water from making it through the liquid and you should inspect further. If you start with cold water it’s harder to guess when the liquid should start flowing out of the tower.
- Check if you can spin the little piston inside the valve and if it moves in and out. If you can move it, it means the pressure can move it too. If you can’t move it with your hands, try a small screwdriver and see if you get get it to move. If it doesn’t, it is likely stuck. Remember, they hold at least 2 bar of pressure so it will take a bit of force to get it moving.
- Sometimes a pressure valve is just worn out and you should get a new pot. However, a worn out valve will highly likely result in steam escaping too quickly instead of keeping it in.
If your safety valve doesn’t move, the first thing to do is to give the whole moka pot a good clean. You can do this by boiling the whole moka pot (except the silicone gasket) in parts a big pot of water with vinegar. That will dissolve most of the deposits everywhere on the pot and in the safety valve. After boiling for a few minutes, rinse the moka pot with fresh water. After that, see if the holes in the filter screens are clear and if the safety valve moves freely now.
If the safety valve still doesn’t move or is stuck open, it’s time to just get a new one. For moka pots from the big brands, you can easily and cheaply find a replacement valve.
If the valve moves after cleaning but doesn’t hold pressure, the O-ring in the valve has probably degraded and become hard/brittle, and moving the valve around has broken it up. Once the O-ring is gone, it’s time to replace the valve. It might seem like cleaning the valve has broken the valve but it’s more likely that the valve and O-ring were already in bad shape and just sealed because of the residue. Once the residue was removed, the valve started leaking.
As you can see knowing how to properly use and maintain a moka pot is more important than with other types of coffee brewing for safety. In the end, with some regular maintenance, a moka pot is safe to use.
Stay safe and enjoy your coffee!
Favorite Moka Pot Products
You don’t need many things to brew good coffee with a Moka pot. Here are the few things you need to make the best possible coffee.
- Moka Pot: Just buy a high quality Moka pot from the get go. The cheaper ones can be messy when brewing. Bialetti is the original and still one of the best with it’s classic looks. They cost a bit more than the cheap ones but these can last for decades and the parts that wear out are easily available for the Bialetti Moka pots. The 3 cup size is good for a single person (Amazon)
- Beans: Good coffee starts with good beans. You can’t make bad beans taste good. Espresso roast beans are good for a Moka pot and will get you closer to that typical espresso taste. Peet’s coffee does a great 100$ Arabica espresso roast. Give it a try, you can get it here on Amazon
- Grinder: Using whole beans means you need to grind them at home. This improves the taste because the grounds are much fresher. A Hario Slim (Amazon) is a great starting point for the starting home barista. If you want a good hand grinder for a good price, check out the TimeMore C2 (Amazon)
- Scales: To get consistent results, a set of accurate scales is essential. Check out this Apexstone scale (Amazon). I’ve been using it for more than a year and while it doesn’t look the sleekest, it’s cheap and just as accurate as more expensive coffee scales. It just reacts a little slower.