How Does Machine Espresso Work?
Machine espresso makes use of precise pressure and incredible filter technology to produce the delicious coffee we enjoy. But how exactly does it work?
Espresso is produced by pushing hot water under high pressure through finely ground coffee. The process is similar to making drip coffee but the difference is in the pressure.
The Group Head
The name implies, the group head is where you place your portafilter when brewing espresso. It is responsible for dispersing water into the portafilter before controlling the pressure of the resulting extraction. There are a variety of group heads, each with its own advantages and disadvantages. Some are focused on temperature stability, others on pre-infusion features, and others are designed to control the lever. There are also some that include a mix of features, like the E61, which is the classic choice among many baristas due to its capacity to offer multiple perks in a single package.
As you can see in the photo above the head of the group has a number of notches. The portafilter is placed into these notches and twist the head to secure it. There is also a gasket made from rubber in the notches and helps create a seal when you insert your portafilter into the machine. The notches allow for precise placement of the portafilter. This is crucial for an accurate extraction.
In addition to allowing you to effortlessly insert your portafilter the group head is also responsible to maintain an even temperature. It does this by circulating hot water through the brew container and around the portafilter, making sure that it is always at the right temperature for extraction. It is important to realize that even a few degree variation can mean the difference between a great and a excellent espresso.
The Pump
Unlike manual piston machines, that use a lever to pressurize water, Rotary espresso machines rely on motorized pumps that provide the nine atmospheric bars of pressure needed to extract espresso. The pressure builds by removing tap water from a reservoir and pumping it through a heat exchanger prior being pumped through the ground coffee in the group head.
Pumps are typically more affordable and last longer than piston-driven machines. However, both types of machines may degrade due to excessive use and insufficient cleaning. They also add mechanical complexity, which can result in a high price tag on even the simplest models.
Certain espresso machines utilize steam pressure instead of a pump to brew espresso. The disadvantage of this is that the boiler that produces steam also raises the temperature of the water to the point of boiling which can cause excessive extraction. Additionally the machines often have to restore their pressure between cups, which requires time and energy.
similar site make use of the rotary or vibration pump, which is a vibration model using a rotating disc to create the pressure and an rotary model that pushes hot water through the grounds at high speed. Both models can produce an excellent espresso, but Rotary machines are quieter and more durable than vibration pumps.
The Boiler
The boiler is the one that will heat the water to the ideal temperature for extraction. The steam that is created will eventually reach the portafilter, which is a container for espresso grounds. The steam is then channeled into the cup. The steam creates enough pressure to push the grounds of the coffee through. This results in a whipped-up top of the espresso. This is a hallmark of a great espresso.
There are three types of espresso makers, which differ in the kind of pump they use and how hot the brew is. There are various ways to control the strength of the brew and the size of cup that can be made by the machine.
The earliest espresso machines were steam-based. They had a single boiler to make both steam and brew however, the pressure they could produce was not very high - 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 producers Luigi Bezzerra & Desiderio Pavoni.
The most commonly used espresso machine is a semiautomatic model with an electric pump. When people think of espresso machines, they picture these machines. With a semi-automatic machine you need to grind the beans and then tamp them yourself but the pump provides regulated water flow and pressure. This is a perfect solution that combines human control with mechanised reliability.
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 essential part of the temperature control system because it stops the machine from overheating.
A filter can also help with flavor since it allows for a longer flowering phase. This lets the beans release their flavor and improves extraction.
It is important to keep in mind that even the most efficient filter can make a bad cup of coffee. The quality of the beans, and the extraction, are still crucial.
This is where the magic happens, it's what makes espresso taste good. The grouphead (also called the brewhead) is where you place the portafilter, which is the thingy used to place the grounds of coffee into when making espresso.
In the steam-driven espresso machine hot water is heated in an airtight container to create steam, which is then pushed through the grounds at a high pressure. These kinds of machines are usually less expensive and easier to maintain than pump-driven models. However, they are not as efficient in their ability to create the perfect conditions for brewing, since they operate at 1-1.5 bars of pressure. The perfect shot requires 9-10 bars.
In recent years, compressed-air-pump-driven espresso machines have been gaining popularity. They make use of an air compressor to force hot water through the ground and are much more mobile than steam-driven electric espresso machines.