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This Week's Most Popular Stories About Machine Espresso
How Does Machine Espresso Work?

Machine espresso employs precise pressure and mind-blowing filter technology to create the coffee we love. How exactly does it work?


Espresso is produced by pushing hot water under pressure through finely ground coffee. The process is similar to making drip coffee. However the pressure is the main difference.

The Head of the Group

As the name implies the group head is where you place your portafilter when making espresso. It disperses water into the portafilter, and then regulates the pressure of the extraction. There are various kinds of group head, each with their particular advantages and drawbacks. Some are designed for temperature stability while others are designed to handle pre-infusion. Others are made to control the lever. There are even some that come with a range of features, such as the E61, which is considered the most popular choice among baristas for its ability to provide multiple benefits in a single package.

As you can see in the photo above the group head is made up of several notches to place your portafilter and twist it by hand to secure it. There is also a rubber gasket in the notches to help create an airtight seal after inserting your portafilter into the machine. The notches on the head allow for an exact location of the portafilter which is crucial to ensure a consistent extraction.

The group head not only allows the portafilter to be inserted easily however, it also keeps the temperature at a constant level. This is accomplished by cycling hot water around the portafilter and through the brew-basket, making sure the temperature is always right to extract the coffee. This is vital, because even a small difference in temperature can mean the difference between good and great espresso.

The Pump

Unlike manual piston machines, which rely on a lever to pressurize water, rotating espresso machines rely upon motorized pumps to deliver the nine atmospheric bars of pressure necessary to extract espresso. This pressure is generated by pumping water through a heat-exchanger and then through the ground coffee.

Pumps are typically less expensive and last for longer than piston-driven machines. However, both kinds of machines may degrade because of excessive use and poor cleaning. They also make mechanically complex which can result in a high price tag on even the most basic models.

Some espresso machines use steam pressure instead of a pump for brewing espresso. The drawback is that the same boiler that produces steam also raises the temperature of the water to the point of boiling which can cause excessive extraction. They also have to constantly rebuild their pressure in between cups. This requires energy and time.

A large majority of espresso machines employ an rotary or a vibration pump. A vibration model employs the vibrating disk to create pressure, whereas a rotating model pushes hot water through the ground at a high speed. Both machines can make great espresso, but rotary machines are quieter, more durable and less likely to break down.

The Boiler

The boiler is the one that is used to heat the water to the right temperature for extraction. The steam created reaches the portafilter, which holds the espresso grounds. It is then poured into the cup. During this process the steam generates enough pressure to push the coffee grounds through. This creates a layer crema on top. This is a hallmark of a great espresso.

There are three distinct types of espresso machines, each having distinct pumps and brew temperature. There are various ways to control the brew and the size of cup that can be made by the machine.

The first espresso machines were steam-types. They used only one boiler to make both steam and brew but the pressure they could produce was very low - just two bars of atmospheric pressure at most. This resulted in the coffee tasting burnt and bitter. This is the reason Milanese makers Luigi Bezzerra and Desiderio Pavoni invented the modern espresso machine.

The most commonly used espresso maker is a semi-automatic machine 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 yourself, but the pump regulates the flow of water and pressure. This is a great compromise between the human touch and the mechanized accuracy.

The Filter

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

It also helps with flavor, since a filter lets you enjoy a longer bloom phase. This lets the beans let their nuances out, and improves extraction.

However, it is important to remember that even a top filter can result in a poor cup of coffee, as the quality of the beans and extraction is still important.

It's here that the magic takes place. This is what makes espresso taste so delicious. The grouphead (also called the brewhead) is where you put the portafilter, the thingy used to place the grounds of your coffee into when making espresso.

In the steam-driven espresso machine hot water is heated in an airtight tank to create steam. Steam is then pushed through the grounds under high pressure. They are less expensive and are easier for the user to maintain than pumps-driven models. They are however limited to create the perfect brewing conditions as they only operate with 1-1.5 bar of pressure. The perfect shot requires 9-10 bars.

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