How Does Machine Espresso Work?

Machine espresso utilizes precise pressure and amazing filter technology to make the perfect cup of coffee. What exactly is it that makes it work?

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

The Group Head

As the name implies the group head is where you place your portafilter when brewing espresso. It is responsible for dispersing the water into the portafilter, and controlling the pressure of the extraction. There are many different types of group heads each with distinct advantages and drawbacks. Some are designed for stability of temperature while others are designed to handle pre-infusion. Some are designed to control the lever. Some come with a combination of both, such as the E61. This is a very popular choice for baristas due to the fact that it has multiple benefits in one package.

As you can see in the above image, the group head has several notches to place your portafilter and twist it by hand to secure it. A rubber gasket is located in the notches to create a seal when you insert your portafilter. The notches on the head allow for an exact positioning of the portafilter which is crucial to ensure an efficient extraction.

In addition to allowing you easily insert your portafilter, the group head is also responsible to ensure that the temperature remains even. It does this by circulating hot water through the brew container and around the portafilter to ensure that it's always at the correct temperature for extraction. It is important to realize that even a tiny variation can mean the difference between a decent and a excellent espresso.

The Pump

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

Pumps are generally cheaper and last longer than piston-driven machines. However, both kinds of machines may degrade due to excessive use and insufficient cleaning. They also increase the complexity of mechanical systems that can lead to a high price tag on even the most basic models.

Some espresso machines make use of steam pressure instead of a pump for brewing espresso. The disadvantage of this is that the boiler that produces steam also raises the temperature of water until it reaches boiling which could lead to over-extraction. They also have to constantly rebuild their pressure between cups. This requires energy and time.

A large majority of espresso machines employ the rotary or vibration pump. A vibration model utilizes a vibrating disk to generate pressure, whereas a rotary model pushes hot water through the ground at a fast speed. Both models can produce an excellent espresso, but the rotary models are quieter and more durable than vibration pumps.

The Boiler

The boiler is the component that heats the water to the optimal temperature to extract. The resulting steam is then transferred to the portafilter containing the ground espresso coffee and is then pumped down into the cup. The steam causes pressure to push through the grounds of the coffee. This results in a whipped-up the top of the espresso. This is one of the hallmarks of a good espresso.

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

The earliest espresso machines were steam-based. They employed one boiler to make both brew and steam, however the pressure they were able to produce was very low - just two bars of atmospheric pressure at most. This led to the coffee tasting bitter and burnt. The modern espresso machine was designed by the Milanese makers Luigi Bezzerra & Desiderio Pavoni.

The most popular espresso maker is a semiautomatic machine that has an electric pump. When people think of espresso machines, they picture these machines. If you have a semi-automatic machine you must grind the beans and then tamp them by hand. However, the pump provides regulated water flow and pressure. This is a great solution that combines human control with mechanized accuracy.

The Filter

Espresso machines usually use a filter that separates the grounds of the coffee from hot water. The filter is also a vital part of the temperature control system because it stops the machine from overheating.

A filter also improves flavor, as it permits a longer flowering period. This allows the beans to let their nuances out, and also allows for better extraction.

However, it is important to remember that even a high-quality filter could result in a bad cup of coffee, since the quality of the beans and extraction is still crucial.

This is where the magic happens, it's the thing that makes espresso taste good. The grouphead, sometimes called the brew head, is the place where the portafilter (the container you place the coffee ground into) sits when you're making espresso.

Steam-driven espresso machines make use of hot water heated in an airtight container to create steam. The steam then pushes hot water through the coffee grounds under high end espresso machine pressure. They are 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, as they only operate at 1-1.5 bars of pressure, while the perfect shot requires 9-10 bars.

In recent years, espresso machines driven by compressed air-pump have become increasingly popular. They use an air-compressor to push hot water across the ground, and are more mobile than steam-driven electric espresso machines.