Joni Helminen
// 21.11.2019

Espresso machine - How does it work?

Have you ever wondered how espresso machines work? What makes the pressure so that you are able to brew espressos with 9 bars of pressure? Our master technician Joni explains the basics of espresso machine and also how you can maintain your espresso machine's durability. 

Espresso machine is working as an extend of baristas arms. Its duty is to offer 9 bars of water pressure to make espresso and steam to froth your milk. Simply put, professional machines can be divided to two different categories how their boilers are designed. 

Heat exchange boiler 

HX boiler
Water diagram of a HX boiler used on espresso machines.

The most common type of espresso machine is with a HX or heat exchange boiler. Basically, there is a coffee boiler that is wrapped with a steam boiler. The water used to make the espressos is heated by the steam boiler and that’s why it´s called heat exchange boiler. In HX boiler machine’s groups are heated with coffee water circulating from heat exchange to the groups and back. That is called convention when temperature difference makes the water to move inside the machine. Benefits of HX boiler is that there is minimal temperature difference between shots because the heat mass and because of their simplified build. Another advantage is that there isn’t that much parts that need service or maintenance. This is how espresso machines have been built since the first espresso machine.

Dual boiler

dual boilers
Nuova Simonelli Aurealia wave dual boiler espresso machine from inside.

Dual boiler machine means that the water used to brew the espressos and the steam boilers are separated and they both have their own heating elements and you can adjust both of them separately. In dual boiler machine you are able to adjust the temperature of water so that it suits best for your coffee. Some baristas like the steam pressure to be a bit lower and it’s possible to adjust the steam pressure without affecting your coffee water temperature. Powerful heating elements also make sure that there is always on demand hot water with minimal temperature difference between shots.

There is always the same amount of water in every espresso, have you ever though how it’s possible? Water goes through a waterwheel that has magnets on its wings. One complete circle equals to one cubic centimeter of water. When there is enough water gone through the waterwheel, the machine knows to stop the flow of water and pump.

espresso machine waterwheel
Espresso machine's water counter compared to small measuring jug.

The pressure pump gives the 9 bars of water pressure for you to brew the espressos and 9 bars is a lot! Baristas’ duty is to control that pressure by making coffee puck tight by tamping the coffee. So it’s really critical to make it right. Not misaligned, right grind size and tamped so the puck is nicely formed. If any of these components are incorrect water finds the easiest way to go through which is also called channeling. 

Why you shouldn’t use the machines hot water to serve tea? Hot water is not taken from the coffee water side, but from the steam boiler. Water in the steam boiler can sit there for ages so most likely it tastes quite horrible. It’s recommended to use hot water just to heat the cups (preferably not even that), not make drinks. 

Technology goes forward every year even if the main principles have stayed the same quite some time. For example, on every Nuova Simonelli’s espresso machine there is a technology called SIS, Soft Infusion System. The system helps the barista on everyday life by correcting any errors while making the coffee puck (e.g. tamping). It slowly ramps the pressure on the start of espresso brew and this way levels the puck. If you have a Nuova Simonelli’s espresso machine, try making espresso without tamping, you will be surprised how close to a perfect espresso it is.

How to keep your espresso machine in top-notch condition?

Making annual maintenance is the best way to keep your espresso machine in a top-notch condition all year around. Water filters are the most cost efficient to reduce service bills, because one of the most common reasons to maintenance is calcification of the espresso machine. Even the best espresso machines need maintenance from time to time. Symptoms that tell you that your machine needs maintenance:

  • Your grouphead is leaking water while brewing. Grouphead gaskets needs to be replaced. The job that can be done also by yourself, ask next time your technician some tips how they can be changed.
  • Steam wand is leaking, or the wand feels stiff. Machine needs descaling or steam wand gaskets need to be replaced. Usually steam wand that is near to your grinder wears much faster than one on other side because most likely it’s used more for practicality. 
  • Hot water tap or steam wand is leaking water. This is usually the first symptom that there’s limescale build up in the espresso machine’s boiler so the boiler needs to be descaled.
  • Grouphead is dripping water even if not used. Usually the espresso machine needs descaling, but try to clean the machine couple of times in a row. There might be just some dirt on coffee three way valve.

Espresso machine that is maintained regularly, can last easily 10 or even more years. Espresso machines cost quite a bit so it's really worth keeping a good care of it. Also of course it's better for your espressos' taste as well. :)

Joni Helminen
Joni in his natural environment.

I'm Joni Helminen, I have been espresso machine technician for over ten years. I would describe my myself a coffee geek, so it has been always my dream job mixing my passion towards coffee and technical knowledge.