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How Does Machine Espresso Work?

Machine espresso uses precision pressure and incredible filter technology to produce the perfect cup of coffee. What exactly does it work?

Espresso is made by forcing hot water at high pressure through finely ground coffee. The process is similar to making drip coffee but the key difference is in the pressure.

The Head of the Group

As the name implies, the group head is where you place your portafilter while making espresso. It disperses the water into the portafilter and regulates the pressure during the extraction. There are many different kinds of group head, each with their own advantages and disadvantages. Some focus on temperature stability, whereas others on pre-infusion capabilities, and still others are designed to control the lever. There are also some that contain a variety of features, like the E61 one, which is to be the most popular among baristas due to its capacity to provide multiple benefits in one package.

As you can see in the image above the group head is made up of several notches where you place your portafilter before twisting it by hand to lock it in. A rubber gasket is located inside the notches, which helps create a seal as you insert your portafilter. The notches on the head permit an exact location of the portafilter which is necessary to ensure a consistent extraction.

In addition to allowing you to easily connect your portafilter, the group head is responsible for maintaining an even temperature. This is done by cycling hot water around the portafilter, and through the brew-basket, making sure that the temperature is at the right level for extraction. This is vital, because even a few degrees can mean the difference between good and great espresso.

The Pump

Motorized pumps in espresso machines that rotate provide the nine atmospheric bar pressure needed for espresso extraction. This is different from manual piston machines that use levers. The pressure builds by drawing tap water from a reservoir, and pumping it through a heat exchanger before being shot through the ground coffee inside the group head.

Pumps are generally cheaper and last longer than piston-driven machines. However, both kinds of machines can deteriorate because of frequent use and insufficient cleaning. They also add mechanical complexity and can lead to an expensive price for even the most basic models.

Certain espresso machines utilize steam pressure instead of a pump to make espresso. This can lead to over-extraction as the boiler that makes steam also causes the water to boil. The machines also need to continually rebuild their pressure between cups. This requires energy and time.

A majority of espresso machines use either a rotary or vibration pump, with a vibrating model using a vibrating disc to generate the pressure and rotating models that push hot water through the grounds at high speed. Both machines can produce excellent espresso however rotary machines tend to be quieter, more durable and less likely to fail.

The Boiler

The boiler is the one that heats the water to the right temperature for extraction. The steam that is produced gets to the portafilter which is the container that holds the barista espresso coffee machine coffee grounds. It is then poured into the cup. During this process the steam generates enough pressure to push the grounds of the coffee through. This creates a layer crema on top. This is one of the main characteristics of a great espresso.

There are three distinct types of espresso machines, each having a different type of pump and brew temperature. There are many ways to control the strength of the brew and the size of cup that can be made by the machine.

The first espresso machines were steam-types. They utilized one boiler to make both steam and brew, but the pressure they could produce was not very high end espresso machine - two bars of atmospheric pressure, at most. This led to the coffee tasting burnt and bitter. The modern espresso machine was designed by the Milanese manufacturers Luigi Bezzerra & Desiderio Pavoni.

The most common espresso machine is a semiautomatic model with an electric pump. These are what people imagine when they imagine an espresso machine. With a semi-automatic machine you have to grind the beans and then tamp them by hand, but the pump regulates the flow of water and pressure. This is a great compromise between the human touch and the mechanised consistency.

The Filter

Typically, espresso machines use filters to separate the grounds of coffee as they move through the hot water. The filter is also an important element of the temperature control system, as it keeps the machine from overheating.

Filters also aid in flavor as it allows for the beans to flower for a longer period of time. This allows beans to release their nuances and gives an opportunity to improve extraction.

However, it is important to keep in mind that even a top filter can produce a bad cup of coffee, since the quality of the beans and extraction is crucial.

This is where the magic happens, it's the thing that makes espresso taste good. The grouphead (also called the brewhead) is where you place the portafilter - the thingy used to place the grounds of coffee into while making espresso.

Steam-driven espresso machine sale machines make use of hot water that is heated in an airtight container to make steam. The steam then moves hot water through the grounds of the coffee under pressure. These kinds of machines are generally less expensive and easier to maintain than pumps-driven models. However, they are not as efficient in their ability to produce the ideal brewing conditions, since they operate at 1-1.5 bars of pressure. While the perfect shot requires 9-10 bar.

In recent years, compressed-air-pump-driven espresso machines have been gaining popularity. They utilize an air compressor to force hot water through the ground. They are also more mobile than electric steam-driven espresso machines.