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How Does Machine Espresso Work?

The machine espresso makes use of precise pressure and filter technology that is awe-inspiring to make the coffee you love. How exactly does it work?

Espresso is made by forcing hot water under pressure through finely ground coffee. The process is similar to that of making drip coffee. However the pressure is the primary difference.

The Group Head

As the name implies the group head is where you insert your portafilter when brewing espresso. It is responsible for dispersing the water into the portafilter and then controlling the pressure of the extraction. There are many different types of group heads each with its own advantages and drawbacks. Some focus on temperature stability, while others on pre-infusion capabilities, and still others are designed to control the lever. There are also some that come with a range of features, such as the E61 one, which is the standard choice for many baristas for its ability to offer multiple perks in a single package.

As you can see in the above image, the group head has several notches where you put your portafilter, then twist it with your hands to lock it in. A rubber gasket is located in the notches to make a seal when you insert your portafilter. The notches on the head permit an exact position of the portafilter which is essential to ensure an even extraction.

In addition to allowing you to easily insert your portafilter, the group head is also responsible to ensure that the temperature remains even. This is done by cycling hot water around the portafilter, and through the brew-basket, ensuring that the temperature is at the right level to extract the coffee. This is vital, because even a small difference in temperature can mean the difference between good and excellent espresso.

The Pump

Unlike manual piston machines, that use a lever to pressurize water, rotary espresso machines rely on motorized pumps to deliver the nine atmospheric bars of pressure that are required for espresso extraction. The pressure is built by pumping water through a heat exchanger and then through the ground coffee.

Pumps tend to be less expensive and last longer than piston-driven machines. However, both kinds of machines can deteriorate because of excessive use and insufficient cleaning. They also create mechanical complexity and can lead to a high price tag on even the simplest models.

Some italian espresso machines machines do away with the pump completely and make use of steam pressure to make espresso. The disadvantage of this is that the same boiler that produces steam also raises the temperature of water until it reaches boiling which can cause excessive extraction. The machines must also continually rebuild their pressure between cups. This requires energy and time.

Many espresso machines utilize an rotary or vibrating pump, which has a vibration model using a vibrating disc that generates the pressure and rotating models that push hot water through the grounds under high speed. Both models can make a great espresso, but the rotary models are quieter and more durable than vibration pumps.

The Boiler

The boiler is the element that heats water to an ideal temperature to extract. The steam produced gets to the portafilter which is the container that holds the espresso coffee grounds. It is then funneled into the cup. The steam is able to create enough pressure to push the grounds of the coffee through. This creates a layer crema that is then poured over. This is a hallmark of a great espresso.

There are three different types of espresso machines, each having different pumps and brew temperature. There are also different ways in which the brew can be controlled and the size of the cup that the maker can create.

The first espresso machines were steam types. They used a single boiler to make steam and brew, however the pressure they were able to create was minimal - two bars of atmospheric pressure at most. This resulted in the coffee tasting burnt and bitter. The modern Espresso machines home machine was developed by the Milanese makers Luigi Bezzerra & Desiderio Pavoni.

The most commonly used espresso maker is a semi-automatic one with an electric pump. These are the images people have when they think of an espresso machine. Semi-automatic machines require you to grind and tamp the beans by yourself while the pump controls the water flow and pressure. This is a great compromise between human control and mechanised consistency.

The Filter

Typically, espresso machines utilize filters to separate the grounds of coffee and espresso machine as they move through the hot water. The filter is also an essential component of the machine's temp control, as it prevents overheating.

A filter can also help with flavor because it allows for a longer flowering phase. This lets the beans let their nuances out, and also allows for better extraction.

It is important to keep in mind that even the most efficient filter can make a bad cup of coffee. The quality of the beans and the extraction, are still very important.

It's here that the magic happens. This is the reason why espresso tastes so delicious. The grouphead, sometimes referred to as the brew head, is the place where the portafilter (the thing you put the coffee ground into) is placed when you're making espresso.

Steam-driven espresso machines use hot water that is heated in an airtight container to produce steam. The steam then moves hot water through the grounds of coffee under high pressure. They are less expensive and easier for the owner to maintain than pumps-driven models. They are however limited for creating the ideal brewing conditions as they only operate with 1-1.5 bar of pressure. The perfect shot requires 9-10 bars.

In recent years, compressed air pump-driven espresso machines have become more popular. They make use of an air compressor to force hot water through the ground, and are more mobile than steam-driven electric espresso machine with frother machines.