How Do Espresso Machines Work?

How do espresso machines work? The process is simple:

Water -> Pump -> Boiler -> Group Head.

As I said, this is a simple process, however, there are a lot of parts and a lot of science involved.

Here in The Coffee Arsenal, we make an effort to create the most comprehensive guides about coffee gear.

In this article, we will show you the full workflow of an espresso machine and how the parts involved work together to make the elixir of life, an espresso shot.

Keep reading to discover how espresso machines work.

The Classic Espresso Machine Workflow

Let us be clear about something: There is not an “espresso bean”. Espresso shots are the result of a work of engineering and technical knowledge. Any ground coffee can become an espresso after receiving the right treatment.

Every espresso machine has a procedure to prepare coffee in the best possible way. It all starts from the water used in the preparation until the final product. 

Despite how simple the mechanism seems, the process is water treatment to get the flavor from ground coffee beans.

1. Water 

The process starts when the water gets into the machine.

On the other hand, if coffee demand is high, it is better to use water from a constant source. The plus side of these machines is that you do not have a tank to fill. Instead, you can plug it into tap water. 

Usually, it is recommended to make sure water is clear to avoid malfunctions.

However, espresso machines like the E61 model offer a mix between the previous two. 

It draws water from the constant source and deposits a part pre-heated or pre-treated. Ready to use to make coffee. You must clean the water deposit to avoid fungus formation.

2. Pump

The pump is a part that pushes water through ground coffee to get the flavor and aroma from it. The water needs to get about 130 PSI to compress the coffee in the desired way. Nowadays, there are mainly two types of pumps in an espresso machine.

The first one is the rotary vein pump. This is a mechanical pump that uses small veins in a spinning device that while rotating makes enough pressure. The device has the shape of a disk and it spins giving pressure that the espresso machine needs.

On the other hand, there is the vibratory pump. It is more sophisticated than the previous kind of pump. It uses a magnet attached to a piston inside a coil. After receiving electric power, the piston pushes water through the machine at a pace of 60 pushes per second.

Both pumps have advantages and disadvantages. In the case of the vibratory pump, they are easy to change. Also, they are smaller and inexpensive in comparison with the rotary vein pump.

However, rotary vein pumps give more consistent pressure and they are more silent. This is a relief for the coffee shop attendants who feel annoyed by the machine’s noises. In addition, rotary pumps have a longer lifespan than vibratory pumps.

3. Boiler

Boiling water is a safe way to eradicate most undesired microorganisms from it. Most common bacterias do not survive high temperatures. Heated water also gives us a way to extract the flavor from ground coffee. But, how hot must it be?

Boiler espresso machine

3.1 Heat

Pressure and heat turn ground coffee into a powerful espresso. The heat starts with a simple electric resistance that sets the water on the deposit at the desired temperature. 

The bigger the deposit is, the hotter the resistance needs to get. As well, the bigger the boiler is the more coffee it produces.

3.2 Temperature Control

To get a coffee well done might be luck unless you have a formula for that. Espressos are not different in that sense. You can have the right amount of ground coffee and water but without the right temperature, it is just luck.

Most espresso machines use one of two pieces for temperature control: PID and Digital temperature control. PID stands for Proportional Integral Derivative. It is a computer that works an algorithm to ensure water is at a certain temperature.

You can find the PID connected to the heating element like the electric resistance, and it reads temperature constantly. That is the way the PID helps the espresso machine to control the temperature of the water for some machines.

On the other hand, the Digital Temperature Control does the same but lets you read less information about the temperature. You can see more information on a screen on your PID than on the panel of a Digital Temperature Control.

In other words, Digital Temperature Control switches between on and off to keep temperature according to an algorithm. Unlike the PID, the user can program the Digital Temperature Control at will. Both devices give the machine a tasty standard espresso.

4. Steam Wand

We can’t continue talking about how espresso machines work without talking about the steam wand.

Espresso machines have an alternative to “simple coffee”. Since machines use water near the boiling point, they produce steam. 

The average temperature of the boiler for brewing is around 90°C – 95°C. Always below the boiling point.

This steam is necessary to prepare lattes or cappuccinos, so the steam wand is as important as the texturized milk. Keeping a part of the water boiling to produce steam and keeping some to brew coffee is a challenge.

However, there is more than one way to solve this problem. The three most used solutions are next.

4.1 Single Boiler 

Single boilers are the lower-cost alternative, but it has two major inconveniences. The first is obvious: you can not have water boiling and not boiling at the same time. The second is a consequence of the first inconvenience: you must wait until the water is at the right temperature.

4.2 Heat Exchanger

This is a simple way to have water ready to serve at the right temperature for boiling and steam. A copper tube serves as the heat exchanger. The tube passes through the boiler, heating the water in it, always supplying water.

That way while the boiling water produces steam, the water from the heat exchanger reaches the brewing temperature. Then you have both steam and brewing water ready to serve at the same time. 

The temperature of the brewing water in this system is harder to measure. Therefore, you might have overheated or underheated.

It is recommended to purge the water out of the copper tube so you have better control of the water in it. This process is recommended right before brewing coffee.

4.3 Dual Boiler

It is the perfect system for producing large amounts of coffee. It uses two different boilers on different deposits. Then you will have one boiling for steam and one ready to brew always. 

It uses a PID or a Digital Temperature Control to ensure the right temperature for each water supplier.

The biggest advantage is the control over the formula you will have with this system. Additionally, you can produce more coffee by using a dual boiler than using the previous two systems. 

Nevertheless, as it has more components than others, dual boilers are more expensive. However, if you plan to use it in a high-traffic coffee shop, it pays itself regardless of the high cost.

5. Group Head

This is the final stage of the coffee before filling the cup. It is a piece formed by the portafilter, the lock for the portafilter, the pump activator, and the water exit. 

This piece is considered the heart of the espresso machine. Also is referred to as the espresso machine “group”.

Group head espresso machine

Types of Group Heads

Let us focus on three types of group heads. The most common, of course. These are Model E61, the Saturated model, and the Semi-Saturated model.

Model E61

This is the model that probably is the best for performing maintenance. With its 9 pounds of weight and made mostly of brass, E61 performs perfectly. However, it takes about 15 minutes to get to the right temperature.

Once it reaches the proper temperature it can maintain it longer than other group heads. Also, this group head requires more attention and participation from the user. In other words, if you start the machine, you decide when to stop the machine. Full control of the machine.

The process of the water serving starts when the outer chamber on top of the group head is full. Then, the water contained passes to the water intake nozzle called “Gicleur”, and later to the brewing channel. As long as the brew lever is down, there will be no water flowing to the rest of the head group.

Once you start lifting that lever, water begins to move to two places. A part goes to the deposit where the ground coffee is. The other part goes down to the pre-infusion chamber. At this point, the main valve is not still activated. 

Since the E61 model is entirely manual, the user can control how much time the water will be in the pre-infusion chamber. It helps to make easier expresso, but not a “better espresso”. 

Lastly, when the lever is completely up, pressurized water starts flowing through the machine. Then it is time for the pressurized hot water to move to the ground coffee to make the espresso. 

Model Saturated

The name comes after the main characteristic of the entire process. This group head lets water flood the entire piece saturating it, therefore it gets the name from this characteristic. 

Since the water boils in the group head there is no need for a brass tube to supply water at the right temperature.

This piece is a three-way valve. One of the ways is a copper tube attached to the water intake nozzle. This copper tube goes attached to all the systems to a rubber gasket and a mini-computer.

The second piece of the three-way valve is a copper tube that leads water to the dispersion block. After that, the almost boiling water fills the bed where the ground coffee lies. Once the machine is on, pressurized water gets the espresso out of the machine to the cup.

The third valve serves only as a “waste line” to help the machine to get rid of excess water. 

After the espresso shot is served, the pump stops and two of the three-way valves are closed. The only valve opened is the waste line which helps to relieve pressure from the machine.

In a general way, Saturated group heads are more delicate to fix and to get maintenance. The usual recommendation is to get this maintenance done by a well-trained technician. This is the most used for commercial purposes.

Model Semi-Saturated

In more than one way, Semi-Saturated woks are similar to Saturated group heads. The main difference between both is that Semi-Saturated has separated areas for the boiler and the dispersion block area.

For anything else, it works essentially similar to the Saturated model. However, Semi-Saturated group heads are less expensive to repair and produce. So in terms of rentability, they are perfect. 

Extra: The Portafilter

A portafilter is a small metal basket designed to fill with ground coffee. There are two common standard portafilters: the 53mm and the 58mm portafilters. Make sure it fits the size of the tamper. Otherwise, the coffee will not compress the ground coffee properly.

Other Types of Espresso Machines

  1. Pour Over Espresso Machines: It is a small espresso machine that can hold a small amount of coffee. It is perfect for those who live alone or maximum for a couple living together.
  2. Plumbed-In Espresso Machine: Unlike the previous machine, it is designed to serve many people. Hence it should have a water supply running constantly.
  3. Volumetric Espresso Machine: This machine will allow you to automatically control the amount of water in your espresso. This greatly affects the flavor and the aroma. Here, you must set the water volume on your machine before it brews.
  4. Lever Espresso Machines: Its lever allows controlling the pressure on the water flowing through the coffee grounds. This is especially good for the most customized coffee.
  5. Pod Espresso Machines: They are based on ground coffee pods. The most practical way to serve coffee is by using coffee pods. This is a popular and easy way to make an espresso and also is the fastest way.
Modern espresso machine

How do Manual Espresso Machines Work?

Hot water and pressure are key to getting an espresso. So manual espresso machines are activated by a lever that controls how much pressure you add to the brew. So in other words, you fill the coffee deposit and the hot water, and your grip does the rest.

There are many different kinds of manual espresso machines, but all have in common the lever. They are good for customizing your coffee shot.

How do Automatic Espresso Machines Work?

Once you get the coffee in its place, you just need to switch “on” the machine to get an espresso. The different pressure devices mentioned earlier are similar among them. In the sense of reaching a pressure of 130 PSI, they are all the same.

So there is no need for a lever to add pressure to the coffee. This type of machine gets it from steam and mechanical features. Automatic espresso machines make it easier for you to brew while attending to many things at the same time.

How do Pod Espresso Machines work?

First, you must load the tank with water, then switch “on” the boiler. After that, you must put the coffee in its place to receive pressurized hot water. So far all the process is the same as with manual or automatic espresso machines.

The main difference is the need for pods of coffee to make it work. These are small cup-like pods that contain the coffee. After the water goes through the pods, the resultant espresso drips into the cup. 

How Do Stovetop Espresso Machines Work?

The genius of this espresso machine comes from its simplicity. This is also called the “Moka Pot” due to its shape and function. It does not have a bunch of pieces and does not require electric power.

The stovetop machine is a 3 part pot machine gathered all together by a thread in the middle section. Inside the bottom, you only put water and in the middle, you put the ground coffee.

Later, you put the top and then twist it until it is closed. Then you put it to boil on the stove and wait for the noise and the smell. When water boils on the bottom section it pushes water upwards, straight to the coffee. 

When all water is boiled the top section will have the brew ready.

The Bottom Line: How Do Espresso Machines Work

Now you understand how espresso machines work.

The water pump, the boiler, the group head, and the portafilter, all of these are essential gears in the process of making the perfect espresso.

Leandro Santorsola
Leandro Santorsola

Leandro is the founder of The Coffee Arsenal. His favorite relaxation method is to drink a Cafe Latte in the afternoons.