How Does Machine Espresso Work?
Machine espresso utilizes precise pressure and incredible filter technology to produce the perfect cup of coffee. How exactly does it work?
To make an espresso, hot water is pushed under pressure through finely ground coffee. The process is similar to making drip coffee. However, the pressure is the primary difference.
The Group Head
As the name implies, the group head is the place you place your portafilter when brewing espresso. It distributes water into the portafilter and regulates the pressure of the extraction. There are various kinds of group head, each with their particular advantages and drawbacks. Some are focused on temperature stability, while others on pre-infusion features, and others are designed to control the lever. espresso coffee machine are a combination, like the E61. This is a preferred choice for baristas as it provides a variety of advantages in one package.
As you can see from the picture above the head of the group has a number of notches. You place your portafilter inside these notches, and then twist the head to secure it. There is also a gasket made of rubber in the notches to help create the seal when you insert your portafilter into the machine. The notches allow for the precise placement of the portafilter. This is crucial for an even extraction.
In addition to allowing you to easily place your portafilter in, the group head is responsible for maintaining a consistent temperature. It does this by cycling hot water through the brew container and around the portafilter, ensuring that it's always at the right temperature to extract. This is important because just a few degrees could mean the difference between excellent and great espresso.
The Pump
The motorized pumps that are used in espresso machines rotary provide nine atmospheric bar pressure that is required for espresso extraction. This is different from manual piston machines that use levers. The pressure is created by drawing tap water from a reservoir and pumping it through a heat exchanger prior being shot through the ground coffee inside the group head.
Pumps tend to be less expensive than piston-driven models, and they tend to last longer, however both types of machine can become damaged due to excessive use and poor cleaning. Pumps are also more complex mechanically, which could increase the cost of even simpler models.
Some espresso machines remove the pump entirely and employ steam pressure to create espresso. The downside is that the same boiler that produces steam also raises the temperature of the water until it reaches boiling which could lead to excessive extraction. In addition these machines typically have to rebuild their pressure between cups, which requires time and energy.
Many espresso machines utilize an rotary or vibrating pump, with a vibration model that uses a vibrating disc to create pressure, and a rotary model pushing hot water through the grounds under high speed. Both types of machine are capable of producing excellent espresso, however the rotary models are quieter and more durable than vibration pumps.
The Boiler
The boiler is the one that is used to heat the water to a temperature that is ideal to extract. The steam that is produced is then directed to the portafilter, which is a container for espresso grounds. It is then funneled into the cup. In this process, the steam creates pressure to push through the grounds of the coffee. This results in a layer crema on top. This is the hallmark of a great espresso.
There are three kinds of espresso makers. They differ in the kind of pump they use and how hot the brew is. There are many ways to control the brew and the size of cup that can be made by the machine.
The earliest espresso machines were steam type. They utilized only one 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 burned. This is why the Milanese makers Luigi Bezzerra and Desiderio Pavoni created the modern espresso machine.
The most well-known espresso machine is a semiautomatic one with an electric pump. These are the things people think of when they think of an espresso machine. 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 great compromise between the human touch and the mechanized quality.
The Filter
Typically, espresso machines have a filter to separate out the grounds of coffee when they pass through the hot water. The filter is also a crucial component of the temperature control system, as it keeps the machine from overheating.
Filters also aid in flavor, as it permits a longer flowering period. This allows the beans to release their nuances, and also allows for better extraction.
It is important to keep in mind that even the most efficient filter can result in a bad cup of coffee. The quality of the beans and the extraction process are still crucial.
This is where the magic happens, and it's what makes espresso taste great. The grouphead (also known as the brewhead) is where you put the portafilter, the thingy used to place the grounds of coffee into while making espresso.
In a steam-driven espresso machine, hot water is heated in an airtight tank to produce steam, which then pushes the hot water through the grounds at a high pressure. They are less expensive and easier to maintain than pumps-driven models. However, they are limited in their ability to produce the perfect conditions for brewing, since they are only operating at 1-1.5 bars of pressure. While the perfect shot requires 9-10 bars.
In recent years, espresso machines powered by a compressed air compressor have become increasingly popular. They make use of an air compressor to push hot water across the ground. They are also more mobile than steam-driven electric espresso machines.