How Espresso Machines Work & Their 5 Main Parts - Complete Guide

In this detailed guide, we go through how espresso machines work, closely examining the main espresso machine parts and their related functions.

Have you been looking to buy an espresso machine but are overwhelmed with all of the different options? There are so many types and features to choose from that analysis paralysis can quickly set in.

While the espresso machine was developed in Italy during the 1800s, the technology has come a long way since then. These machines come with pumps, boilers, group heads, grinders, hoppers, etc…

But what does it all mean? What components should you pay attention to during the buying process?

Grab a coffee and let’s get into it.

What is an Espresso Machine?

If you stumbled across this article, you probably already know that espresso is a rich and concentrated coffee served in small shots with a layer of crema on top. But how does an espresso machine actually produce this delicious beverage?

Put simply, an espresso machine uses a large amount of pressure to send hot water through a tamped-down puck of finely ground espresso beans.

In this breakdown, we focus on the more traditional style of machines known as semi-automatic espresso machines. 

Semi-automatic machines differ from automatic and super-automatic espresso machines because the brewer is still responsible for grinding and tamping the coffee. You also have more control over the length of the total brew, subsequently affecting how much water you use.

Automatic and super-automatic espresso machines generally don’t allow for as much customization over the process because they can automate brew time, grinding, and even the tamping of the beans.

Check out our other article for a breakdown of these different types of espresso machines.

Regardless of the type, modern espresso machines are mostly pump-driven.

How Espresso Machines Work

There are five main parts of an espresso machine that pump-driven, semi-automatic (or manual) espresso machines have and these parts are:

1. Water Source
2. Pump
3. Boiler
4. Group Head
5. Steam Wand

Each component has a specific function and purpose. Let’s make sense of the espresso machine by going through each one.

The Five Main Espresso Machine Parts

1. Water Source

Espresso is made up of only two ingredients: finely ground coffee and hot water. It’s no secret that water is important to pulling a quality shot.

Espresso machines can either come with a reservoir for water or have a direct line into the building’s water supply. There are pros and cons to each, but using a direct line (or plumbed-in) style allows for a large number of drinks to be made with an endless supply of water.

Home espresso machines tend to use reservoirs.

Most commercial espresso machines are plumbed in and hooked to softening and filtration systems to purify the available tap water into the ideal water for brewing coffee. Filtration is key!

There are also hybrid models available with both, giving you the option to start with a reservoir and expand to a direct line later. 

Whatever the case, water needs to be pulled into the espresso machine to be pressurized, heated, and used for pulling a shot of espresso.

2. Pump

The pump is what circulates water through the entire device. You can think of it as the heart of the espresso machine, moving water through various vessels like our hearts move blood through our veins and arteries.

The pump is responsible for creating the needed pressure to brew espresso, 9 bars of pressure (130 psi) to be exact.

You will find two main types of electric pumps in today’s espresso machines: vibratory pumps and rotary vane pumps.

Vibratory Pump

A vibratory (or vibe) pump uses an electromagnet to generate pressure. In this pump, a magnet sits inside a metal coil. When electricity is sent through the espresso machine, the magnet moves a piston back and forth at an average of 60 pushes per second.

Rotary Vane Pump

Unlike a vibratory pump, a rotary vane pump is mechanical. A motor spins a disc that is offset inside a round chamber. When the disc spins, it presses several tubes (or veins) into the sides of the chamber, creating high pressure to move water.

Vibratory pumps are cheaper than rotary pumps, but they require more maintenance. Vibe pumps also generate more noise.

Rotary pumps provide more consistent pressure and have a longer lifespan than vibratory pumps.

Both pumps work great, so you shouldn’t worry too much about which kind your future espresso machine comes with.

3. Boiler

Now that the pressure is generated, you might wonder how the water is heated to the correct temperature. That’s where the boiler comes in, heating water to brew the espresso and produce steam for the steam wand.

The boiler’s job is to take pressurized water coming from the pump and heat it up to the right temperature for brewing and steaming.

How exactly is this temperature regulated? There are two ways to control how hot the machine makes water.

Pressurestat

Simpler, more inexpensive home espresso machines tend to come with a device called a Pressurestat to regulate the water temperature. It controls temperature by detecting pressure, but it doesn’t actually measure temperature itself like a thermometer.

If pressure is too high or too low, it acts as a switch that turns the heating element on or off. (1)

They are automatically calibrated to a specific pressure (and consequently a related temperature) that can’t be later changed. Because of this, they aren’t great at pulling consistent shots.

PID or Digital Temperature Control

A PID, or proportional-integral-derivative controller, gives you more control over the brew temperature. Essentially, a PID is a mini computer that controls a heating element to keep the water at a specific temperature. 

It’s connected to both the heating element and a temperature probe located inside the boiler. The readings are done in real-time, allowing for constant adjustments.

It does this using an algorithm that turns the element on and off to accurately reach and hold the desired temperature.

Digital temperature controls work very similarly to PIDs, but they don’t allow you to adjust the algorithm. The digital display on PIDs also tends to have more information than those on digital temperature controls.

Now that you understand how the temperature is dialed in, let’s talk about how and where heat is generated: the boiler.

There are three main types of boilers found in espresso machines:

• Single Boiler
• Heat Exchanger
• Dual Boiler

Single Boiler

Single-boiler espresso machines have one heating element to heat the water. Because the temperature needed for brewing espresso is much lower than for steam, there is a necessary wait time between pulling shots and steaming milk.

Heat Exchanger

Machines with heat exchangers attempted to solve this problem, while still maintaining a single heating element. In a heat-exchange system, the water heated is boiled and only used to make steam.

In order to get the right temperature of water for brewing espresso (which is much lower than for creating steam), an additional line is run from the pump and connected to a copper tube that is inside the boiler.

Water in the boiler passes around the copper tube, heating up the water inside the tube without boiling it.

While this method sounds great and eliminates the waiting period between brewing and steaming like in single-boiler machines, it can be hard to control the temperature. Overheating is a common problem.

Dual Boiler

This is the best option for most espresso machines and the one that most coffee shops use. One boiler is used exclusively to heat water for brewing, while the other is used only to heat water for steaming milk.

Almost all commercial machines will have two boilers in order to quickly serve customers and meet high demand during busy hours.

4. Steam Wand

While we are on the topic of temperature, let’s quickly address steam wands. 

While not a crucial component to the actual making of espresso, steam wands let you make heated and textured steamed milk to create espresso-based drinks like cappuccinos, lattes, and flat whites.

While many places around the world have a culture of drinking espresso plain, adding milk is a popular trend in countries like the United States and Canada.

Steam wands work by introducing hot air into milk at a very high speed. They inject air rapidly into the milk, breaking the surface and folding that air into the liquid. This creates a frothier texture while also heating the milk up to the right temperature.

Steam wands can’t be used while brewing espresso on machines with a single boiler. You need a heat exchanger or dual boilers in order to perform both tasks at the same time without a waiting period.

5. Group Head

The last part of the espresso machine is actually a collection of various pieces, valves, and nozzles. The group head is the final component that water passes through, finally reaching the ground coffee and creating a shot of espresso.

There are four basic parts that comprise a group head:

• Portafilter: A portafilter is an espresso tool that holds a basket full of finely ground, tamped coffee beans. It is indeed a filter and traps the coffee grounds when pulling the shot, able to withstand high pressure, only letting hot water and coffee oils through. The most common sizes are 53mm and 58mm.
  
  
  
• A place for the portafilter to lock into: This spot securely connects the portafilter to the group head via a gasket to ensure there are no leaks during the high-pressure extraction.
  
  
  
• A spot to turn on the pump: Whether this is done with a mechanical lever or an internal computer, the group head will have some mechanism in it that signals for the pump to turn on and off, starting or stopping pressure.
  
  
  
• Channel for water to go from boiler to portafilter: The hot water has to make its way from the boiler to the coffee grounds, and these series of channels and valves in the group head will direct it there.

While all group heads share these parts, how they function depends on the specific type in your espresso machine. There are three main types of group heads:

• E61
• Saturated
• Semi-saturated

E61 Group Head

Some of the most reliable and popular espresso machines come with the E61 group head. It was invented in 1961 by Ernesto Valente and has definitely stood the test of time.

These group heads are made entirely out of brass and are extremely heavy. They are built to last.

While it takes 20-25 minutes to heat up (2), once the group head is at the desired temperature, it remains very stable.

The E61 can be thought of as a three-way, mechanically-operated valve.

In one valve, water travels from the boiler into the group head. In the second value, hot water is sent from the group head to the portafilter and coffee grounds. The third valve acts as a way to release back pressure from the portafilter once the espresso shot has been pulled.

When the water is introduced to the coffee grounds via the second valve, a “pre-infusion” of sorts is happening. Hot water is introduced to the tamped puck of coffee grounds without any added pressure. This gives the grounds time to stabilize with the hot temperature before the pump turns on and brings 9 bars of pressure.

Some say this pre-infusion helps give a better taste in the final shot. You use the mechanical lever to control how long you want this stage to be.

When you pull the lever into the “up” position, the pump is then activated. Bringing it back into the “down” position turns the pump off and opens the drain valve, releasing any pressure from the portafilter basket and drying the spent puck of coffee grounds.

Saturated and Semi-Saturated Group Heads

Saturated and semi-saturated group heads have direct access to the boiler. This allows them to heat up quicker than the E61.

Semi-saturated group heads have an area that is separated from the boiler just above the dispersion block, while saturated heads are open to the boiler.

These group heads are also three-way valves like the E61, but they are controlled by tiny internal computers. They work similarly and can also be programmed for pre-infusions.

Saturated heads are more common for commercial espresso machines, while semi-saturated group heads are more common in machines for home use. 

Other Parts of an Espresso Machine Worth Noting

Of course, an espresso coffee machine is not only made up of 5 parts. It has other sections that are necessary for the coffee machine to function. Here's a quick list:

• Bean Hopper
• Power Switch
• Pressure Gauge
• Grinder and Adjustment Dial
• Drip Tray
• Hot Water Tap

Related Articles:

• The Best Breville Espresso Machine + Other Contenders
• Best DeLonghi Espresso Machine -Ultimate Buying Guide
• The Best Portable Espresso Maker + Other Contenders
• How to Properly Clean and Descale Your Espresso Machine!

Frequently Asked Questions

Final Thoughts

There’s no doubt that espresso machines are very complex beasts. There’s a reason for the hefty price tag compared to other coffee gear. 

We hope that you better understand the anatomy of an espresso machine, how espresso machines work, and can identify the different espresso machine parts and functions.

If you are in the market for a semi-automatic espresso machine, you are now equipped with the knowledge you need to make a smarter purchase decision.

Like all hobbies, once you dive deeper into how something works, you develop a bigger appreciation for the end product… in this case, a rich and complex shot of espresso.

Happy brewing!