Structure and Functionality of an Espresso Machine

Structure and Functionality of an Espresso Machine

Espresso machine – definition of a device

An espresso machine, usually in the form of a portafilter coffee machine, is a device that is suitable for brewing espresso and other coffee specialties. But how exactly does an espresso machine work? In it, water is heated to around 90 degrees Celsius and pressed through finely ground coffee under a pressure of around 9 bar, the pressure being generated either by a lever or an electric pump. So that the flour is not whirled up in the brewing chamber, the ground material is pressed firmly with a tamper (also called “espresso masher” or “coffee masher”). 

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A little history of the espresso machine

As early as the 19th century, various designs were patented for making espresso using a machine. In these first attempts, the pressure was never strong enough. It was not until 1938 that Giovanni Achille Gaggia registered a patent for a piston system that was able to force water through coffee powder under high pressure. The result was an espresso with a frothy crown, the so-called “crema”. Nevertheless, Angelo Moriondo is considered the official inventor, who in 1884 filed a patent for a machine that included the use of steam and water. From the 1950s onwards, numerous smaller manufacturers in Spain and France also designed espresso machines. The first portafilter coffee machine in Germany for private use came on the market in the 1950s with the name “Aracati” from the manufacturer “Acosta”.

The components, functions and tasks within the espresso machine as a portafilter construction

Portafilter machines are hybrid forms between professional espresso machines and fully automatic coffee machines. They can be operated manually or work fully automatically. They score particularly well with their large setting and variation options. The basic functionality is the same for all portafilter machines. However, the structure and individual parts may differ.

A. The pump as the heart of the portafilter machine

It is not only responsible for directing the water from the tank into the brewing unit, but also enables the hot water to flow powerfully through the coffee groundsThe optimal pressure for the process is 9 bar, even if many manufacturers indicate higher pressure values. These specifications are correct in that they refer to the maximum output of the pump pressure of the pump if it should not be possible to reduce the pressure.

B. The boiler

When making this choice, it is advisable to focus on your drinking habits in advance. Do you only want to enjoy espresso with the machine, or do you also want to use other types of coffee?

1. The single circle

In such espresso machines, a kettle forms the core that supplies both brewing groups and steam lances at the same time. The expert understands the “steam lance” to be a stainless steel nozzle that brings hot water vapor under the surface of the milk and in this way creates extremely fine-pored milk foam. Unless you only want to make espresso, such a construction is not very suitable. Because the optimal temperature for the brewing groups is 90 degrees Celsius. However, if you now want to prepare a cappuccino, for example, you will need milk foam. For the creation of the steam required for this, far more than 100 degrees Celsius needed. However, since two different temperatures cannot exist in one water circuit at the same time, the temperature of the boiler must be adjusted by heating up when changing the brewing water to steam. A portafilter machine with a single circuit is not necessarily an optimal choice for the production of different coffee beverages.

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2. The two-circle

The functionality of the dual circuit solves this bottleneck. Because a kettle with hot water for rich steam for frothing the milk forms the first water cycle with temperatures of over 100 degrees Celsius. This encloses a small water chamber into which fresh water flows from the tank or the water supply. As it passes through the hotter steam boiler, the water is heated to the ideal brewing temperature, which is determined by the combination of the cycle time and the ambient temperature is determined. This means that brewing water and steam can be drawn off at the same time without waiting. If the machine is not used for a long time, the water in the chamber takes on the temperature of the steam boiler, which is far higher than the temperature required to make an espresso. This is important to note if you have not made an espresso for a long time ! You can solve such a problem by draining water over the brew head, because this way the chamber is refilled with fresh, cold water before the brewing process.

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3. The dual boiler

This construction is relatively new in the world of coffee. Two separate boilers for brewing water and steam enable new dimensions of capacity and control. Espressi and steam can be produced at the same time with professional machines with the dual boiler without having to worry about fluctuations in pressure and temperature. The temperature and pressure of both circuits can also be individually adjusted.


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C. The brew group

The brew group is also important for the quality of the drink. This is where the Italian company FAEMA sets the trend-setting standard with the “E61” model. This brewing group consists of three elements. A special mechanism consisting of valves and springs allows the remaining pressure to be diverted after the brewing process. There is also the option of a so-called “pre-infusion”. Here, hot water does not immediately hit the ground coffee with high pressure, but a small amount of water beforehand strengthens it with little pressure and allows it to swell. Furthermore, there is also the element of the thermo syphon system. It is important within the brew group as a kind of hot water heater. A water cycle is directed from the boiler through the brewing group with the result that it is always optimally heated. Only if the water is not used for a long time due to the rare production of espresso, it can overheat, so that it has to be filled with cold, fresh water beforehand.


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The espresso machine is suitable for making espresso and other types of coffee. Whether you choose the boiler in the form of the

  • Single circle
  • Two-circle
  • or the dual boiler

depends on your preferences when it comes to enjoying coffee.