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How Does Machine Espresso Work?

Machine espresso makes use of precise pressure and mind-blowing filter technology to make the perfect cup of coffee. But how exactly does it work?

To make an espresso machine small, hot water is pushed under pressure through finely ground coffee. The process is similar to making drip coffee, however the main difference lies in the pressure.

The Group Head

The group head is the portafilter you place in the espresso maker when making it. It is responsible for dispersing water into the portafilter and controlling the pressure of the resulting extraction. There are numerous kinds of group heads, each with its own advantages and disadvantages. Some focus on temperature stability, whereas others on pre-infusion features, and others are designed to control the lever. There are even some that contain a variety of features, like the E61 that is to be the most popular among baristas because of its ability to provide multiple benefits in one package.

As you can see from the above photo, the group head is fitted with a variety of notches. You place your portafilter into these notches and twist the head to lock it. A gasket of rubber is situated inside the notches to help create a seal while you insert your portafilter. The notches permit precise placement of the portafilter. This is crucial for a consistent extraction.

Aside from allowing you to easily insert your portafilter, the group head is also responsible to maintain an even temperature. It does this by cycling hot water through the brew pan and around the portafilter to ensure that it is always at the right temperature to extract. It is important to note that even a tiny differences can make the distinction between a good and great espresso.

The Pump

The motorized pumps that are used in espresso machines that rotate provide the nine atmospheric bar pressure needed to extract espresso. This is different from manual piston machines that use a lever. The pressure is created by pumping water through a heat exchanger and then through the ground coffee.

Pumps are generally less expensive and last for longer than piston-driven machines. However, both kinds of machines can deteriorate because of excessive use and poor cleaning. Pumps are also more complex mechanically, which can increase the cost of even the simpler models.

Some espresso machines employ steam pressure instead of a pump for brewing espresso. The drawback is that the boiler that produces steam also raises the temperature of water until it reaches boiling which can cause over-extraction. Additionally the machines often have to rebuild their pressure between cups, which requires time and energy.

Many espresso machines utilize an rotary or vibrating pump, with a vibrating model that uses a vibrating disc to generate the pressure and the rotary model pushing hot water through the grounds at high speed. Both machines can make great espresso but rotary machines are more stable, quieter and less likely to break down.

The Boiler

The dual boiler espresso machine will heat the water to a temperature that is ideal to extract. The steam produced gets to the portafilter which contains the espresso coffee grounds. It is then funneled into the cup. During this process the steam creates enough pressure to push the coffee grounds through. This results in a crema on top of the espresso. This is the hallmark of a good small espresso machine.

There are three types of espresso machines, each with different pumps and brew temperature. There are various ways to control the amount of brew, as well as the size of the cup that can be produced by the machine.

The first espresso machines were steam-type. They had one boiler to make both steam and brew, but the pressure they could generate was low - only two bars of atmospheric pressure, at most. The coffee tasted bitter and burned. The modern espresso machine was developed by the Milanese producers Luigi Bezzerra & Desiderio Pavoni.

The most popular espresso maker is a semi-automatic machine with an electric pump. When people think of espresso machines, they imagine these machines. With a semi-automatic espresso machine, you must grind the beans and tamp them yourself but the pump controls the flow of water and pressure. This is an excellent solution that combines human control with mechanised reliability.

The Filter

Espresso machines typically have filters that separate the grounds of coffee from hot water. The filter is also a vital part of the machine's temperature control, since it stops overheating.

It also helps with flavor, since a filter allows for a longer bloom time. This helps the beans to let their nuances out and provides an opportunity for better extraction.

However it is crucial to remember that even a good filter could result in a bad cup of coffee as the quality of the beans and extraction is still crucial.

It's here that the magic happens. This is the reason why espresso tastes so good. The grouphead, also referred to as the brewhead, is where the portafilter (the container you place the ground coffee in) is located when you're making espresso.

Steam-driven espresso machines use hot water heated in an airtight vessel to create steam. The steam then pushes hot water through grounds of coffee under high pressure. They are less expensive and are easier for the user to maintain than pumps-driven models. They are however limited in their ability 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 use an air compressor to push hot water through grounds and are significantly more portable than electric steam-driven machines.