How Do Espresso Machines Work?

You’ve had a few on your wish list for a while and you’re finally ready to bring one of those beautiful espresso machines home for yourself.

But where do you start? Even if you make your own pour over coffee at home, espresso seems like a different beast altogether. There are so many questions to answer. What is a boiler? What does ‘9 bars of pressure’ mean? Is that good? How does an espresso machine work?

In this guide, we’re going to look at how a semi-automatic espresso machine works so you can bring your espresso machine home with confidence.

Dialling in Your Lingo – Key Terms to Know

First, let’s take a look at some key terms to know when talking about espresso machines.

• Dialling in – Dialling in is coffee jargon for tweaking certain parameters of the brewing process in order to get the best result. When brewing espresso, this might entail adjusting the grind size, tamp, or amount of coffee used.
• Portafilter – The portafilter is where you put your ground coffee. It’s exactly what its name suggests – a filter. When making espresso, water is (hopefully) forced through the portafilter at the ideal pressure and ideal temperature to produce decadent espresso.
• Tamp – Tamping is compressing the coffee into the portafilter so that the water doesn’t flow right through the coffee grounds. A good tamp creates the necessary restriction, prevents water channeling, and helps to dissolve more solids. (1)
• Bars of Pressure – A bar is the unit of measurement for the pressure at which your coffee is extracted. Common knowledge suggests that a proper espresso needs to be extracted at 9 bars of pressure, which is 130 PSI — or over four times as much as a car tire! (2)

Now that you’re speaking the language, let’s take a look at the different parts of your home espresso machine.

Water and Pump

You can’t have espresso without water, right? In an espresso machine, water either comes from a small reservoir where water is poured, or from a connected water line. You can find home espresso machines that utilize either.

But how do we get that water through the espresso machine? The pump does all the work here. Because brewing espresso means to extract coffee at 9 bars of pressure, a pump is needed to create pressure that forces the water through the coffee at the right pressure.

There are two main types of pumps. Vibration and rotary pumps. Rotary pumps are more commonly used in commercial machines and provide a constant supply of pressure. Vibration pumps are more likely to be found in your espresso machine at home and only create pressure when pulling an espresso shot. Unless you’re really geeking out, you might not notice a difference, except that vibratory pumps tend to be a lot noisier. (3)

Boilers

The boilers are some of the most important espresso machine features to look at. For espresso, just like any other coffee, your water needs to be at the optimal temperature to allow for proper extraction. And your boiler is how it’s going to get there. Water is fed into the boiler through a one-way valve, where it is collected and heated.

There are 3 main types of boilers in a semi-automatic espresso machine: single boiler, double boiler, and heat exchange.

Single Boiler

A single boiler is exactly what it sounds like. Water for both brewing espresso and steaming milk is collected and heated in one single tank.

The problem with a single boiler is that you cannot brew espresso and use the steam wand at the same time. The ideal temperature for steaming milk and the ideal temperature for brewing espresso are drastically different. Using the same boiler for both means having to wait for the water to heat up or cool down after using each function before you can move on to the next one. This is a bit of a pain when you’re trying to make a latte and your espresso starts getting cold as you wait to steam the milk.

Single boilers are usually only found in low-end automatic and semi-automatic espresso machines.

Heat Exchange

A heat exchange boiler is also one large boiler, except it has an isolated section within the boiler that’s separate from the main heating element. The isolated section in a heat exchanger provides water that is cooler and suitable for brewing. This is achieved by continuously supplying water through the isolated element, into the group head, and back down into the machine.

The ability to heat water to different temperatures means that you don’t have the wait time between using your steam wand and espresso shot pulling as you do with a single boiler.

Dual Boiler

Similar to the single boiler, a dual boiler is very appropriately named. Espresso machines with a dual boiler have 2 separate tanks instead of one that does all the work. One tank heats water for brewing while the other heats water for steaming.

A dual boiler means that you don’t need to wait for the water temperature to change. The two separate boilers not only allow you to steam milk and brew simultaneously, but it’s also the best option for temperature stability since each tank can be held at the appropriate water temperature.

If you want to steam milk and pull a shot at the same time, a dual boiler is the way to go.

Related: Dual Boiler vs Heat-Exchanger

Group Head

This is pretty much where the magic finally happens. The group head is the part on the front of your espresso machine where the portafilter locks into place.

When you pull an espresso shot, the valve seats open and the group head sends pressurized, hot water from your espresso machine, through your compacted coffee, and out the bottom of your portafilter, creating espresso.

When buying an espresso machine, you may encounter 1 or 2 group options. This is just telling you how many parts of the machine you can pull espresso from. For your home set up, you’ll likely only need a single group head.

Final Thoughts

There you have it. After this look under the hood, you hopefully have a better understanding of how an espresso machine works, and you now realize the investment required. Though the process of running hot water through compact coffee sounds simple, there’s a lot going on in these little machines. Your next task? Learning how to make an espresso drink!

Did you find the inner workings of the espresso machine to be more complicated than you originally thought? Are these machines more simple than you figured they’d be? Let us know!