How Do Espresso Machines Work? 

For many of us, coffee is an essential component of life.  In fact, there is nothing that a good cup of joe cannot fix. 

However, has it ever occurred to you to stop and wonder how to make this delicious drink? Of course, we know espresso machines brew coffee, but I do not think many of us understand what goes through that process. 

To put it simply, all espresso machines need to do is to push hot water through a puck of finely-ground coffee. 

It is that simple, but the tangles of wires and hulking metal can intimidate most users to the point that it can put them off from learning the intricacies of this machine. 

If you are curious about what it is like, this article will show you what constitutes an espresso machine and how everything goes and ties together to make a steaming cup of delicious coffee. 

To start, here is an overview of the parts you see in espresso machines

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

As you can see, the article will follow how water moves through the espresso machine – starting from its source down to the portafilter. 

 

Water Source

brewing coffee

 

Espresso machines need water for them to brew coffee. 

Most espresso machines get water either from a built-in water reservoir or via a plumbed connection to the main water source. 

The type of water source you get depends on how you will use your machine. 

For example, espresso machines with built-in water reservoirs are ideal for brewing a cup or a small batch of coffee. 

These types also give the user more freedom as you can easily tweak and adjust the water quality. 

On the other hand, if you plan to brew large batches of coffee daily, then an espresso machine with a plumbed-in connection is essential. 

The steady water supply entails that you wouldn’t have to get up and refill constantly. 

There are also hybrid espresso machines that have both a built-in reservoir and a plumbing option. 

If you are not sure which method works for you, you can try these hybrid versions to get a feel of what works best. 

Aside from the type of water source, remember also to pair it with a water filter. 

The best coffee brews are made of clean and clear water. 

Water with too much or too little mineral content will adversely affect its taste. 

 

breville water source

Water Reservoir 

Pros: easier to adjust, easy to set up and clean 

Cons: need to refill, needs routine cleaning and maintenance 

Machines: Rancilio Silvia M Home Espresso Machine, La Pavoni “Stradivari”

Plumbed-in 

Pros: no need for constant refills 

Cons: needs to be set up, set up might be expensive 

Machines: Isomac TEA Espresso Machine, Vibiemme VBM Domobar

 

Pump 

pump

 

Consistent pressure is needed for water to push through a bed of finely-ground coffee and extract the rich flavors. 

The espresso machine should have a pressure of at least nine bars to get a perfect shot of espresso. 

How the machine generates pressure depends on the type it is.  

They are usually classified into lever-driven machines and pump-driven machines. 

In the former, the espresso machine comes with a lever that you need to push down to extract the espresso. 

On the other hand, the latter relies on an electronic pump to generate pressure and is what you usually find in home-based espresso models. 

Pump-driven machines usually have the following pumps: rotating and vibrating. 

Rotating Pumps 

Rotating or rotary pumps have a motor and rotor to create that pressure. 

The spinning motor causes the veins inside the disc to press against the outer chamber. 

As a result, the space shrinks. 

Hence, the pump pushes out the water every time this disc shrinks.  

Rotary pumps are usually found in professional-grade espresso machines. 

These types of pumps deliver consistent pressure and are quick in reaching different pressures too. 

Rotary pumps are also quite large and are more robust, and thus, they are more adept in handling larger volumes of water. 

They are also quiet when operating and have longer lifespans. 

 

coffee machine pump2

Vibrating Pumps 

Vibrating or vibratory pumps utilize a pulsating piston to gather water from the tank and then push it through the boiler. 

The piston moves at an average of sixty pushes per second. 

These pumps are usually found in home espresso machines since they are smaller and are quite simple. 

Vibratory pumps are also affordable and are less susceptible to limescale build-up since they are suited to lower volumes of water. 

However, vibratory pumps are often unstable in delivering pressure which can affect your brew. 

Rotary Pump 

Pros: quiet operation, consistent pressure, long lifespan 

Cons: bulky and large 

Machines: La Spaziale S1 Vivaldi II Espresso Machine, Nuova Simonelli Musica Espresso Machine

Vibratory Pump

Pros: affordable, small, less susceptible to limescale build-up

Cons: inconsistent pressure, loud, short lifespan 

Machines: La Pavoni “Napolitana” Espresso Machine, Rancilio Silvia M Home Espresso Machine

 

Boiler 

coffee machine pump

Heating is an essential element in an espresso machine. 

After the water pushes through the ground coffee, it is time for the machine to heat it. 

Like water pressure, the temperature also needs to be consistent to get a delicious espresso shot. 

The boiler is the component responsible for heating the water in the machine. 

However, boilers can get a little complicated. 

Aside from the size, boilers often come with extra features to promote stability and user control. 

To avoid confusing you, we are going to be discussing each feature. 

Boiler Size 

larger coffee machine

The larger the boiler, the more batches it can brew. 

However, remember that more coffee batches mean that the espresso machine requires more time and energy to brew them. 

Plus, there might be a bit of waiting time in between. 

Small Boiler 

Pros: more compact, easy to set up, affordable

Cons: limited coffee brews

Machines: Gaggia Classic Semi-Automatic Espresso Machine, ECM Casa V Espresso Machine

Mid-size Boiler 

Pros: ideal for most users, has the most product variations

Cons: has the most product variations

Machines: Quick Mill Silvano Evo Espresso Machine, La Spaziale S1 Mini Vivaldi II Espresso Machines

Large Boiler 

Pros: brews large batches 

Cons: expensive, requires a lot of energy 

Machines: La Marzocco GS3 Espresso Machine Original Automatic

Boiler Types 

The next factor is how many boilers you will use. 

Again, this factor will depend on how you will be using your espresso machine. 

Single boilers 

Single boiler

Single boilers only have one boiler that both brews espresso and steam for milk. 

Their simple build means that these boiler machines are usually inexpensive. 

However, since they only have a single boiler, you cannot brew and froth milk simultaneously. 

You will have to wait for the espresso machine to finish brewing before you can froth. 

Moreover, there is a bit of waiting time before you can steam milk since you will have to wait for the machine to reach the correct temperature. 

It is not a problem if it is only a single drink, but the waiting time can add up if you are brewing several milk-based beverages. 

Dual boilers 

dual boiler (1)

Dual boilers utilize two boilers – each having a heating element. 

As such, dual boiler espresso machines can brew espresso and steam milk simultaneously. 

The extra boiler increases the price of these machines, but you will get the convenience of brewing numerous milk-based drinks. 

 

Heat exchange 

Heat exchange machines also have a single boiler, but they can brew espresso and steam milk at the same time. 

How? 

These machines keep the water at a steaming temperature instead of boiling it. 

Although it can simultaneously brew and steam, heat exchange espresso machines are more affordable than dual boilers. 

However, brewed water can overheat if left for too long, making it difficult to control the brewing temperature. 

Users recommend purging tiny quantities of water in timed intervals; however, this has a learning curve most users will have difficulty adapting to. 

Single boiler 

Pros: affordable 

Cons: long waiting times, cannot brew and steam simultaneously 

Machines: ECM Casa V Espresso Machine, Quick Mill Carola Espresso Machine

Dual boiler 

Pros: brew and steam simultaneously, precise temperature control 

Cons: expensive 

Machines: Rancilio Silvia Pro Double Boiler Espresso Machine, Lelit PL92T Elizabeth V3 Dual Boiler Espresso Machine

Heat exchange 

Pros: brew and steam simultaneously, less expensive option 

Cons: Difficult to control the temperature 

Machines: Kalerm KLM1601 Premium Super Automatic Espresso Machine, Rocket Appartamento Espresso Machine

 

Boiler Temperature and User Control Options 

coffee machines buttons

The secret of making a good shot of espresso is to have consistent temperature and pressure. 

Hence, it is not far off to say that little spikes or inconsistencies with temperature can affect the espresso’s taste. 

Luckily, espresso machines now have various features that can help the user control and stabilize temperature. 

Pressure stat 

Most compact and affordable espresso machines use a pressure stat that sets the brewing temperature to a certain number. 

The advantage this gives is that it is ideal for beginners or for those who simply don’t want a lot of fuss over their coffee. 

You will just need to run the machine and wait for your coffee. 

However, this also means the user cannot control or adjust the temperature accordingly. 

As a result, the espresso machine might brew inconsistent shots, especially when used frequently. 

Proportional integral derivative (PID)

PID or digital temperature control features let the user adjust the brewing temperature. 

Both are essentially the same – the difference lies in how the PID provides more information and control than the digital temperature control. 

Moreover, PID also enables the user to adjust the algorithm, which you cannot do in a digital temperature controller. 

Pressure stat 

Pros: affordable, easy to use 

Cons: inconsistent over time, limited control 

Machines: Bezzera BZ10, ECM Mechanika V Slim

PID 

Pros: enables precise temperature control

Cons: not that durable 

Machines: Quick Mill Silvano Evo Espresso Machine, Lelit PL91T Victoria Espresso Machine

 

Group Head 

coffee grounds

The group head is the last component water goes through in an espresso machine. 

It is a metal attachment and is the place where water meets the puck filled with coffee. 

When it is time to pull an espresso shot, the group head gets pressurized water, sends it through a diffusion plate, and finally to the portafilter filled with ground coffee. 

While there are various group head types, they essentially have the same parts – just in different configurations. 

This section will discuss the three types of group heads available. 

E61 group head 

The E61 group head was named after the year it was patented by the company, Faema. 

Now, this group head is off-patent and thus, found in various espresso machines. 

The E61 revolutionized the coffee world when it was first introduced. 

Due to its brew consistency and user-friendliness, the E61 quickly replaced the large lever espresso machines that were common before. 

For one, the E61 group head was the first espresso machine to have an electric pump, have a thermosyphon, and enable pre-infusion. 

As such, the group head stood out among the various espresso machines fitted with three-way valves in the market. 

Incoming hot water enters through the water inlet, an opening found in the back of the group head. 

The pressurized water then leaves via an exhaust at the bottom. 

The cam is an oval-shaped metal that rotates and presses on the valves at the side, and it is connected to a lever to enable the user to control the brewing process. 

When the lever is down, the group head is switched off. 

The E61 group head is distinct by the fact that it is made from nine pounds of brass. 

This material means that the group head has solid temperature stability as the material takes a while to heat up and cool down. 

Due to its thermosyphon system and heat exchanger, the E61 could only heat the brew by circulating the water within the machine. 

The higher the temperature difference between the brew and the water in the heat exchange, the quicker the circulation. 

These components opened doors for espresso machines to use fresh water in making coffee. 

Lastly, the pre-infusion is possible due to the peculiar shape and structure of the EC61 as it leaves a bit of water in the coffee grounds before the pressure builds up. 

As a result, the remaining moisture causes the ground coffee to “bloom” or “swell up” and solidify and bring out a fuller and richer flavor for extraction. 

 

espresso machine

Saturated group head 

La Marzocco made the saturated group head in 1970. 

It was first featured in the company’s GS machine, being wielded directly onto a brew boiler, and made from brass. 

Saturated group heads are hollow as they have a large reservoir that needs to be filled with water. 

When activated, the hottest water in the boiler would rise to the high part of the group head while the cooler water would run down to the boiler where it can be reheated. 

Once the shot is extracted, the pump deactivates, and the valve closes. 

Early versions of saturated group heads had a high temperature offset between the boiler and the brew temperature since they weren’t insulated. 

Newer versions of this group head already come with foam insulation to reduce this energy wastage. 

Semi-saturated group head 

Semi-saturated group heads are not connected to the boiler as a heat exchanger separates them. 

Hence, these group heads are easier to repair and cheaper to produce. 

However, the downside is that they are slightly less stable in sustaining temperature. 

E61 group head 

Pros: high heat retention, user can control brewing 

Cons: long heat-up time (about 20 minutes to 40 minutes) 

Machines: Bezzera Unica PID Espresso Machine, Izzo Vivi 3 Espresso Machine

Saturated group head 

Pros: long lifespan, computer-controlled, stable temperature 

Cons: high energy cost, costly to produce and repair 

Machines: Slayer Single Group Espresso Machine, Victoria Arduino Adonis Commercial Espresso Machine

Semi-saturated group head 

Pros: easier to repair, cheaper to produce

Cons: less table in temperature maintenance

Machines: Lelit Elizabeth, LUCCA A53

 

Portafilter 

espresso portafilter

The portafilter pertains to the filter basket that contains ground coffee and is in the group head. 

There are various portafilters available that can adversely affect the taste of your espresso. 

Size 

First, they come in different sizes – 58mm, 54mm, 53mm, and even 40mm.

The portafilter’s size largely depends on the manufacturer or brand and is set, meaning you cannot enlarge it or vice versa.

The size also affects the amount of coffee you can place inside. 

Hence, the smaller the portafilter, the less ground coffee you can put inside. 

Basket sizes 

Portafilters also differ by basket sizes which are: 

Single-shot baskets 

Single-shot baskets can only hold eight to ten grams of coffee and are found in smaller or less inexpensive espresso machines. 

They also come with a set of small holes at the bottom to reduce flow speed. 

Double shot baskets 

Double shot baskets are what usually come in standard or mid-priced espresso machines. 

These baskets can hold sixteen to twenty grams of coffee. 

Triple shot baskets 

Triple shot baskets are usually found in professional espresso machines or made for brewing large batches. 

These baskets can hold thirty to thirty-five grams of coffee. 

Single-shot basket

Pros: ideal for individual use, easy to control 

Cons: limited batches 

Double shot basket 

Pros: ideal for a small batch 

Cons: left-over coffee grounds 

Triple shot basket 

Pros: can accommodate and brew large batches 

Cons: left-over coffee grounds 

 

portafilter

Spouts 

Portafilters usually come with spouts so that the espresso would flow from the machine onto the cup. 

However, modern espresso machines also utilize a new type – the naked portafilter. 

Spouted portafilter 

As mentioned earlier, portafilters usually come with one to two spouts for the espresso to flow from the machine and onto the cup. 

Double spouts are quite convenient as you can easily divide the espresso shot into two cups. 

Naked portafilter 

As in its name, naked portafilters have no spouts, which leave the filter basket exposed. 

Hence, you can clearly see the espresso shot flow from the machine into the coffee cup. 

Because of the lack of obstruction, naked portafilters enable the user to monitor their espresso shots carefully. 

For one, you can tell right away when there are tamping errors. 

Knowing your errors can help you improve and make you consistent over time. 

The absence of a spout also makes it easier to clean, and you would not risk affecting the flavor due to oil build-up in a spout. 

Lastly, naked portafilters are also said to produce more crema compared to their counterparts since air particles stay trapped longer. 

Spouted portafilter 

Pros: easier slide, convenient 

Cons: Difficult to clean, oil build-up can affect the taste

Naked portafilter 

Pros: produces more crema, easier to clean, user can notice errors right away 

Cons: messier, has a learning curve 

Pressure 

Non-pressurized portafilter 

Typically, portafilters are not pressurized since the espresso machine itself can generate pressure. 

All you will have to do is press the portafilter down and tamp the coffee. 

Pressurized portafilter

However, some espresso machines come with pressurized portafilters. 

In fact, you can usually see this in super-automatic types or low-level machines. 

Here, the portafilter comes with several holes to generate pressure. 

Pressurized portafilters are quite ideal for beginners since it only needs a gentle tamp. 

However, a set pressure also means that you will have less control over the espresso shot. 

Non-pressurized portafilter 

Pros: inexpensive, convenient 

Cons: difficult to repair 

Pressurized portafilter 

Pros: ideal for beginners

Cons: less control over the shot 

 

Conclusion 

Knowing how the espresso machine works is not necessary, but it makes you appreciate how your cup of delicious coffee came to be.  Moreover, having this bit of knowledge also helps as you now know what parts to tweak and adjust to improve your coffee’s taste. 

It will also come in handy in case the espresso machine ever breaks down and needs a few repairs.  Having this tidbit of information is also useful when you are looking to buy a new espresso machine. 

Lastly, you will know what components to focus on and find an espresso machine that will suit your needs.  Happy brewing! 

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Cuppabean
Charles is the author and managing editor of Cuppabean.com. A self-admitted coffee addict, he drinks 2-4 cups of coffee a day to get his fix. Read more about the site here.

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