How Does Machine Espresso Work?

Machine espresso employs precise pressure and amazing filter technology to make the perfect cup of coffee. What exactly does it work?

In order to make espresso, hot water is pushed under pressure through finely ground coffee. The process is similar to making drip coffee. However, the pressure is the major difference.

The Group Head

The name implies, the group head is where you place your portafilter while making espresso. It is responsible for dispersing water into the portafilter and then controlling the pressure of the resulting extraction. There are a variety of types of group heads each with its own advantages and drawbacks. Some are designed for stability of temperature while others are specifically designed bean to cup espresso machine handle pre-infusion. Some are designed to control the lever. Some have a combination of features, like the E61 one, which is the standard choice for many baristas because of its ability to offer multiple benefits in a single package.

As you can see from the picture above the group head is equipped with several notches. The portafilter is placed inside these notches, and then twist the head to lock it. There is also a gasket of rubber that resides inside the notches, which helps create a seal when you insert your portafilter into the machine. The notches on the head permit a precise position of the portafilter which is vital to ensure a consistent extraction.

The group head not only lets you to insert your portafilter easily however, it also keeps the temperature at a constant level. It does this by circulating hot water through the brew pan and around the portafilter to ensure that it's always at the correct temperature for extraction. It is important to note that even a few degree deviation can make the difference between a good and great espresso.

The Pump

In contrast to piston machines that are manually operated, which use a lever to pressurize water, rotating espresso machines rely upon motorized pumps that provide the nine atmospheric bars of pressure required to extract espresso. The pressure is created by removing tap water from a reservoir and pumping it through a heat exchanger prior to being shot through the ground coffee in the group head.

Pumps tend to be cheaper than piston-driven machines and tend to last longer, however both types of machines can get damaged through overuse and lack of cleaning. They also make mechanically complex which can result in a high price tag on even the most basic models.

Certain espresso machines can eliminate the pump completely and use steam pressure to brew espresso. This can result in over-extraction because the boiler that produces steam also warms the water to boil. The machines must also continually rebuild their pressure between cups. This takes energy and time.

Many espresso machines make use of an rotary or a vibration pump. A vibration model employs the vibrating disk to create pressure, whereas the rotating model pushes hot water through the ground at a fast speed. Both machines can make excellent espresso, but rotary machines are more stable, quieter and less likely to fail.

The Boiler

The boile
It is important to keep in mind that even the best filter can result in a bad cup of coffee. The quality of the beans, and the extraction process are still crucial.

It's in this area that the magic takes place. This is what makes espresso taste so delicious. The grouphead, often called the brew head, is where the portafilter (the device you put the ground coffee into) is located when you're making espresso.

Steam-driven espresso machines make use of hot water that is heated in an airtight container to create steam. The steam then pushes hot water through the grounds of coffee at high pressure. They are less expensive and are easier for the user to maintain than pumps-driven models. However, they are limited in their ability to create the perfect brewing conditions because they operate at 1-1.5 bars of pressure, while the perfect shot requires 9-10 bar.

In recent years, espresso machines powered by a compressed air compressor have become increasingly popular. They utilize an air compressor to push the hot water through the grounds and are more portable than electric steam-driven machines.