How Does Machine Espresso Work?

Machine espresso makes use of precise pressure and incredible filter technology to produce the delicious coffee we enjoy. What exactly is it that makes it work?

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

The Group Head

As the name suggests the group head is the place you put your portafilter in when making espresso. It distributes water into the portafilter, and controls the pressure of the extraction. There are numerous kinds of group heads each with distinct advantages and disadvantages. Some focus on temperature stability, others on pre-infusion capabilities, and still others are designed to control the lever. Some include a combination like the E61. This is a preferred choice for baristas because it offers multiple advantages in one package.

As you can see from the picture above the group head has a number of notches. You can place your portafilter inside these notches, and then twist the head to secure it. A rubber gasket is located inside the notches, which helps create a seal when you insert your portafilter. The notches on the head allow for a precise positioning of the portafilter which is vital for a consistent extraction.

The group head is not just able to allow you to insert your portafilter easily but also maintains a constant temperature. This is achieved by cycling hot water around the portafilter and through the brew-basket to ensure that the temperature is at the right level to extract the coffee. This is important, as just a few degrees could make the difference between a good and great espresso.

The Pump

The motorized pumps used in rotary espresso machines provide the nine atmospheric bars of pressure required for espresso extraction. This differs from manually operated piston machines that employ a lever. The pressure is built by pumping water through a heat exchanger and then through the ground coffee.

Pumps are typically less expensive than piston-driven machines, and they tend to last longer, however both types of machines may be damaged by excessive use and inadequate cleaning. They also add mechanical complexity, which can result in costly prices for even the simplest models.

Certain espresso machines utilize steam pressure instead of a pump in order to brew espresso. This could lead to over-extraction since the boiler that produces steam also heats the water to boil. These machines also have to constantly rebuild their pressure in between cups. This takes energy and time.

A majority of espresso machines utilize a rotary or vibration pump. A vibration model utilizes an oscillating disk to create pressure, whereas the circular model pushes hot liquid through the ground at a fast speed. Both types of machine can make a great espresso, however the rotary pumps are quieter, and more durable than vibration pumps.

The Boiler

The boiler is the element that heats the water to the ideal temperature to extract. The steam produced reaches the portafilter, which is the container that holds the espresso coffee grounds. It is then funneled into the cup. The steam creates pressure and pushes through the grounds of the coffee. This results in a whipped-up top of the espresso. This is a sign of a great espresso.

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

The first espresso machines were steam-type. They utilized a single boiler to make both brew and steam, however the pressure they were able to create was minimal - two bars of atmospheric pressure maximum. The coffee tasted bitter and burnt. The modern espresso machine was designed by the Milanese producers Luigi Bezzerra & Desiderio Pavoni.

The most commonly used espresso machine is a semiautomatic that has an electric pump. These are the things people think of when they think of an espresso machine. Semi-automatic machines require you to grind and tamp your beans yourself, but the pump regulates the water flow and pressure. This is an excellent compromise between human touch and mechanized consistency.

The Filter

Espresso machines usually have a filter that separates the grounds of the coffee from the hot water. The filter is also an important part of the temperature control system as it prevents the machine from overheating.

It also aids in flavor, as a filter allows for a longer bloom time. This allows the beans to release their flavor and improves extraction.

However it is crucial to keep in mind that even a great filter can produce a bad cup of coffee as the quality of the beans and extraction is vital.

This is where the magic happens, it's what makes an espresso really taste great. The grouphead, often called the brew head, is where the portafilter (the thingy you put the coffee grounds into) is placed when you're making espresso.

In the steam-driven espresso machine hot water is heated in an airtight container to produce steam, which then pushes the hot water through the grounds with high pressure. These types of machines are usually less expensive and simpler to maintain than pumps-driven models. However, they are limited in their ability to produce the perfect conditions for brewing, since they operate at machines coffee 1-1.5 bars of pressure, while the perfect shot requires 9-10 bar.

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