How Do Espresso Machines Work?

You’ve probably heard people say that they like their coffee done a particular way. Some individuals prefer a blend of coffee beans that bring into being a unique taste or aroma. On the other hand, a good number of people prefer coffee that has been brewed using a particular type of coffee bean. Nevertheless, the amount of thought put in preparing the coffee is what really matters: whether espresso or regular coffee.

In essence, the style of making coffee is what brings out the “espressoness” in coffee. No particular plant or roasting technique produces espresso beans. However, forcing regular coffee through pressurized water, which then passes through a filter and a “puck” of coffee — that has been ground — to produce coffee that is concentrated and thick, is what transforms regular coffee into espresso.

So, how do Espresso Machines Work?

There are many types of espresso machines. The workings of these machines may differ slightly, on some occasions, but the basics are usually similar. For instance, commercial and top-class home espresso machines have boilers, the difference may arise when it comes to figuring out where the water comes from and why. By reading this article, you will get acquainted with the basics of the workings of these types of machines.

The Boiler

Most espresso machines have a cylindrical copper boiler (the Boiler) with tubes spread over it and a compressor connecting to some of those tubes. The compressor functions as an electric motor that pressures the water running through the tubes. Additionally, a good number of valves and wires plus a few circuit boards also help control how the machine works.

The cylindrical boiler acts as a reservoir for water. The water in the cylinder is usually kept a little more than half full and then subjected to heat from a coil that has been installed in the boiler. A water heat controller is used to measure the temperature in the boiler, and, as a result, water temperature within the machine is kept at a fixed temperature: the heater turns on and off as required.

The Control Circuitry

To ensure that the depth of the water in the boiler is maintained, an electrode is used. To pass current through the electrode, a control circuitry — installed in the coffee machine — regulates the flow of electricity to the boiler. If the water in the coffee brewer falls below the tip of the electrode, the electricity current is disconnected. This prompts the controller to open a valve that allows the flow of water from an external source, say, the plumbing fixture in a building, into the boiler.

It is prudent to note that since the water in the cylinder is pressurised, the external water source must also be pressurised. This means that it should have the force required to push water into the boiler once the valve opens: typically 20 to 30 psi. Once the water touches the tip of the electrode, the control circuitry turns the water intake valve off. The water level in the boiler is therefore kept constant at all times.

The Pressure Gauge

The pressure gauge is used to register the pressure that is inside the boiler and the extraction pressure. The pressure should be maintained at 1.5 bars (indicated on the upper side of the pressure gauge) to produce good steam. If the pressure is lower than 1.5, the espresso machine will not produce good steam. Moreover, if the pressure is higher, it poses a hazard: if the pressure goes beyond 1.8 bars, a safety valve blows.

On the lower side of the pressure gauge, you will see a reading that indicates the extraction pressure of the espresso. The pressure should be kept between 9 and 11 bars: when pulling a shot. Also, when not pulling shots, the gauge reflects water line pressure from the water source.

The Portafilter

The portafilter is a removable part of the machine that is meant to hold the ground coffee. A basket, a handle, and a two-pronged spout have been used to assemble this part of the coffee machine. The coffee is tamped and packed in this section. Thus, the portafilter is fastened to the group head to form a seal. Below the basket, you can find two spouts where the espresso emerges and flows into an espresso cup.
It is prudent to note that the water used to brew the coffee does not come from the boiler, it comes from your building’s water supply: the plumbing system.

How Espresso is Extracted?

The water for brewing the espresso is channelled through a loop that exits the group head, passes via the solenoid valve, through the boiler, and then finds its way back into the grouphead. This process is intended to adjust the flow rate ideally, in a bid to control the temperature of the water in the grouphead. When not pulling a shot, the water pump turns off, and the solenoid valve prevents it from working. However, water flow is maintained.

The reason the water keeps flowing is to ensure the grouphead remains at a constant brewing temperature. This is achieved through Thermo siphoning, a passive physical mechanism. If you chose to record the temperature of the water through the various points, you would discover some insightful revelations. Water is hottest as it leaves the boiler, and then cools down slightly as it approaches the grouphead. As the water exits the grouphead, it loses more heat and is much cooler as it reaches the boiler again. The various changes in temperature allow the automatic flow of water around the circuit, keeping the grouphead hot.

How Water for Coffee is Preheated?

The heat exchanger is quite efficient when it comes to heating limited amounts of water, such as water for a cup of coffee. However, it cannot sustain the flow of heated water indefinitely. As a consequence, the hot water spigot, installed in the coffee machine, utilises water from the cylinder. Home coffee brewing machines, which are meant to be economic do not have boilers. Instead, they have heat exchangers: for steam and espresso. This is why commercial coffee machines have a distinct, rich taste that is not comparable to that produced by the economical home coffee machines.

The Takeaway

The workings of coffee brewing machines are somewhat complicated. However, knowledge of how they work is essential if you are considering purchasing one. The information on how they work helps you find what you are looking for much more effortlessly.

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