Explosions with Espresso Machines

Robert McKeon Aloe
7 min readMay 17, 2019


The first time an espresso machine blew up on me, I thought it was just a rare occurrence. It was not. Now, my machine didn’t blow apart, but it had an explosion of steam. These are the stories of four explosions on three machines and one airplane mishap.

My four electric manual espresso machines ordered by similarity in functionality

The first one happened shortly after buying my Kim Express. I was flushing it a few more times after descaling it with vinegar. I filled it all the way up, and I let it warm up as I read a magazine. I thought I had more time before it warmed up. Usually, the steam release valve would make a certain sound. I did not know that when it is filled to the top, the valve wouldn’t make that sound.

The kitchen where it all started

Instead, the entire 1.5L boiler emptied through the steam release valve in about 30 seconds. My kitchen was only 8x8x8 feet in height, so a cloud formed in my kitchen and then rained on me and the table. I wasn’t embarrassed by the artificial storm in my kitchen, but I was afraid my wife would get mad. I know the boiler completely emptied because when I opened it up, it was bone dry. I could have wrecked the machine.

For the next four years, I did not make this mistake again. Short of ruining a colander to warm up the group element for the Flair Espresso, I did not have a major disaster with respect to my espresso machines even though I had increased my inventory of espresso machines from 2 to 10 as well as the number of shots I had daily. The average age of each of my machines is well above 20 years, so the probability of disaster should be higher.

This is how I preheat now, but I tried a metal mesh with a plastic rim that melted to the pot.

In 2019, I had been taking more data on my espresso shots, and I found I got a bit better performance when the boiler on the Kim was full. I didn’t fill it all the way, and I was cafeful to not make an artificial storm cloud. I had it at work at my desk along side the Enrico of Italy I bought from an old man on a dirty old boat in South San Francisco.

My coffee cart

One day, I had the Kim Express a little too full, and when I pulled the lever to draw a shot, the steam release valve went off. It was impressive in that it caused such a micro storm just over my machine and coffee cart. I suspect an air bubble went from the portafilter to the top and popped the steam valve. However, the boiler did not completely empty. So while I was still a bit embarrassed, I wanted my espresso shot and finished making it as the storm subsided. My friend next to me laughed. I was more afraid I would be told to stop making espresso at my desk. Luckily, few others were in the office to witness the big event.

A month later, a bit after lunch, I decided to pull from my Enrico of Italy. It’s good to remember I bought this machine from a man on a boat off of craigslist. I probably should have inspected it more. I can only pull double shots because I don’t have a single basket, and the baskets are hard to come by (this one fits with some minor adjustments). So I only pull one or two shots a week. They’re beautiful and delicious, but that’s a lot of caffeine for me.

To pull a shot, similar to la Pavoni, you have to take the following steps:

  1. Turn it on, let it warm up.
  2. Bleed the false pressure through the steam wand for 1 minute.
  3. Remove the false pressure from the group head by running a little water through the shower head.
  4. Let it warm up a bit more.
  5. Warm up the group head by running a little water through.
  6. Pull the shot.
A general diagram to help paint a picture of my office setup at the time.

The office was also not empty. My boss and director were in their office across from my pod, my pod had 8 people or so. The wall and door of his office was glass. There was an informal meeting the other direction with 10 people, and the pod next to mine was half full. The office space is semi-open and echos a lot.

I wish I had been recording a video…

I was on step 4 (“Let it warm up a bit more”), and the steam wand blew off of the machine. A six foot horizontal stream of steam went off for what seemed to be eternity but probably more like 10 seconds, as everyone within earshot starred at me. My friends laughed at my obnoxiousness because they all know about my espresso machines. Nobody was hurt, and the steam wand only went two inches onto the table. The initial pop of the wand blowing off of the machine made more the sound than anything else.

Apparently, the wand wasn’t screwed in at all. It was a disaster waiting to happen. There was a locking bolt on the other side, but it had become unscrewed. I had noticed a hissing sound, but I didn’t realize it was foreshadowing the explosion.

Post Accident with missing steam wand.

Normally, this wouldn’t be a big deal at my house, but it was in my office. Everyone within 50 feet heard it pop and stared at me. I had a mix of emotions. On one hand, I was glad I hadn’t put the portafilter on to make the shot because I would have ruined a perfectly good espresso shot. On the other hand, I was embarrassed, but not because I looked like an idiot. I was afraid I would be told to get my espresso stuff out of here and find a new job.

Instead, my boss just laughed. Either he’s used to my eccentricities or it is par for the course for his group. My thoughts were immediately how I need to change jobs now to not have to deal with this situation, how do I discretely clean this up, what story do I tell, and how will I get out of this jam. Luckily, the jam did not exist.

Faema Fun

There’s an old Faema at work, and I wanted to try out my Staccato espresso method. I brought my basket and portafilter. I wasn’t quite sure what the optimal grounds input for the Faema, so I guessed.

I knew I went too far when water started leaking out of the sides of the portafilter instead of the filter. Some coffee was coming out, but then, rather quickly, the portafilter was pushed partially out of the grouphead (the link is to the video).

A total mess ensued, and after cleaning up, I tried again with less. The machine hadn’t had new o-rings in awhile, and I shouldn’t have been able to stress the grouphead that way on a well maintained machine.

Explosions on the Go!

Imagine the white cup in the middle spilling. It’s full of the leftover coffee water and puck.

I’ve also been making espresso on flights for the past year. This can be a tricky process, but usually, it’s the clean up that’s the issue.

I ask for half a cup of hot water for my drink, and I only use a quarter cup for brewing. Then I pour the waste water and the leftover grounds back into the cup. Often, the cup has a lid. On one occasion, I set that cup down on the ground near by bag after making espresso. The kids were a bit wild, and I ended up knocking over the cup.

Dirty coffee water soaked the floor, my bag, and my shoes. I was quite upset in that moment, but I take these risks with espresso because I want good espresso all the time.

If you experiment too much, you’re bound to mess up a few machines. Luckily, the machines are fine, nobody was hurt, only the coffee was lost.

If you like, follow me on Twitter and YouTube where I post videos of espresso shots on different machines and espresso related stuff. You can also find me on LinkedIn

Further coffee readings of mine:

Staccato Espresso: Leveling Up Espresso

My coffee setup

Artisan coffee is overprice

The Tale of the Stolen Espresso Machine

Affordable Coffee Grinders: a Comparison

Espresso : Grouphead Temperature Analysis

Espresso filter analysis

Portable Espresso: A Guide



Robert McKeon Aloe

I’m in love with my Wife, my Kids, Espresso, Data Science, tomatoes, cooking, engineering, talking, family, Paris, and Italy, not necessarily in that order.