What is an espresso machine and how does it work

Understanding the structure of the espresso machine will help you understand the great beverage it extracts. I will teach you everything you need to know about the espresso machine: its structure, how its system works, and how to use this knowledge to perform the extraction technique correctly.

The structure of the espresso machine

The espresso machine is a true jewel of Italian engineering, envied and replicated worldwide.

The structure is very similar to the professional machines in bars and domestic machines. However, professional machines are usually more powerful.

Espresso machine structure
Espresso machine structure

The parts we are most interested in are:

  • The boiler.
  • The boiler pressure gauge.
  • The heat exchanger.
  • The electric pump.
  • The preparation group, the filter holder, and the filter.
  • The hot water tap.
  • The steam wand.

1. The boiler

The boiler is usually made of steel, copper, or brass. It is used to supply hot water, heat it for coffee extraction and create steam for the steam wand.

The water coming from the mains passes through a descaler or cleaner, which eliminates substances unsuitable for preparing espresso coffee, such as limescale, chlorine, etc. At this point, it arrives “clean” to the boiler’s interior (descaling the water), where it is heated and kept at the required temperature for the duration of the service required.

In the boiler, the water reaches temperatures between 230 – 240 °F, with a pressure between 1.1 and 1.4 bar. The boiler must never be full, as steam is formed in the upper part due to the high temperatures.

2. The boiler pressure gauge

The pressure gauge is precisely the part of the machine that is visible to the barista and allows him to check the correct pressure or not inside the boiler, which, as we have just said, must be between 1.1 and 1.4 bars.

3. The heat exchanger

The heat exchanger is the system that heats the water to extract the espresso. We do not use the water from the boiler to prepare the coffee for two reasons:

  • Temperatures are too high. The water in the boiler reaches more than 230°F, while to extract the coffee, we should be between 195 and 205 degrees.
  • The water in the boiler is stagnant. It is true that it comes from the water softener and is therefore free of lime and other substances. Still, it remains in the boiler for a long time at very high temperatures and could therefore create undesirable bacteria or sediments.

It is necessary to imagine a small pipe, generally made of copper, which transports the purified water from the distribution network. This small pipe, passing through the boiler, heats the water inside. In this way, the water used to prepare the espresso is always purified, soft, and fresh.

4. The electric pump

This pump can “compress” the water against the ground coffee with a very high pressure, usually about 9 bar. This is what makes the espresso be considered as such.

Espresso is a very concentrated coffee beverage, dense and with a creamy surface. What makes it possible to create the crema, along with other factors, is the pressure. Without pressure, the crema would not be able to form in the cup.

Think of the Moka pot: even with the best Italian coffee maker in the world and using the same coffee we use for espresso; we would never obtain the same crema as with the espresso machine precisely because of the lack of this great pressure!

5. The brewing group, the filter holder, and the filter

The brewing group is the part to which the filter holder is attached, i.e., the arm that the operator attaches and detaches to introduce the ground coffee and prepare a new coffee.

It has a hand shower, which distributes the water evenly over the ground coffee, and the gasket, which allows the portafilter to adhere completely.

On the other hand, the filter holder is, as we have said, the arm that we hold in our hand with the filter containing the ground coffee inside. The latter, perforated at the bottom, allows the infused beverage to come out.

6. The hot water tap

For example, this component is where the hot water comes out to prepare tea. In this case, in most espresso machines, the hot water from the faucet comes directly from the boiler, not the heat exchanger. Only in some newer machines does the water come out through the heat exchanger system.

7. The steamer

And now we come to the last part of the structure of the espresso machine, the frother: this instrument allows the steam to come out to froth the milk. To do this, it extracts the steam from the boiler and lets it escape.

How the espresso machine works

An espresso machine is a tool that works using an extraction process that combines hot water at high pressure with finely ground coffee to produce a concentrated and delicious beverage.

  1. The brewing process begins by loading the ground coffee into the filter holder of the espresso machine and compacting it.
  2. The filter holder is then placed in the machine head and pressed to ensure a tight fit.
  3. Once the filter holder is in place, the machine begins to heat the water to the appropriate temperature. To obtain between 195°F and 205°C at the heat exchanger, the boiler can reach 240°F.
  4. Once the water has reached the right temperature, the pump pushes the hot water through the ground coffee in the filter holder. The pressure applied can vary depending on the machine but is generally between 8 and 15 bar pressure.
  5. The water is drawn through the coffee for about 25 to 30 seconds, resulting in a thick, creamy beverage.
  6. Once the coffee has been extracted appropriately, the machine stops extraction, and the filter holder is released.
  7. The machine is thoroughly cleaned after each use to maintain the quality of the coffee and ensure that the machine is working properly.

The espresso machine combines high-pressure hot water with ground coffee to produce a full-bodied, intensely flavored beverage with a thick, pleasant crema.

The difference between a professional espresso machine and a domestic espresso machine

The difference between domestic and professional espresso machines lies fundamentally in their size.

The boiler of the domestic ones is smaller. It has more difficulty keeping the water sufficiently hot and at a constant temperature for extraction, providing less steam to froth the milk.

In addition, the structure of the professional espresso machine is heavier and more robust, which allows it to retain better the pressure to extract the espresso to its full potential.

Written by Pablo Barrantes Nevado
I am Pablo Barrantes, a coffee lover. I decided to start this website to solve all the doubts that arise every day when preparing our favorite drink: coffee. I am an industrial engineer by profession, but I have worked in coffee shops for many years, where I have learned all the secrets about coffee machines and coffee. My passion for coffee has led me to investigate and study beyond the obvious, and thanks to this, I can offer solutions and give news about coffee and coffee makers. I hope you enjoy reading as much as I research, document and write here.

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