How Does Machine Espresso Work?
Machine espresso employs precise pressure and incredible filter technology to produce the coffee we love. How exactly does it work?
In best espresso machine 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 main difference.
The Head of the Group
The name implies the group head is the place you insert your portafilter when making espresso. It disperses water in the portafilter, and then regulates the pressure of the extraction. There are several different types of group head each with its particular advantages and disadvantages. Some focus on temperature stability, while others on pre-infusion capabilities, while others are designed to control the lever. Some include a combination like the E61. This is a preferred choice for baristas as it provides a variety of advantages in a single package.
As you can see in the image above the group head is made up of several notches where you put your portafilter, then twist it by hand to lock it in. There is also a rubber gasket which is located inside the notches and helps to create a seal when you insert your portafilter into the machine. The notches on the head permit an exact positioning of the portafilter which is essential to ensure an efficient extraction.
Aside from allowing you to easily insert your portafilter, the group head is also responsible for maintaining a consistent temperature. This is accomplished 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 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 which use levers. The pressure is built by pumping water through a heat-exchanger and then through the ground coffee.
Pumps tend to be cheaper and last longer than piston-driven machines. However, both kinds of machines may degrade due to overuse and insufficient cleaning. Pumps are also more complicated mechanically, which could increase the price of even the simple models.
Some espresso machines eliminate the pump completely and instead utilize steam pressure to make espresso. The downside is that the boiler that produces steam also increases the temperature of water to the point of boiling, which can lead to excessive extraction. In addition these machines are often required to restore their pressure between cups, which takes time and energy.
Many espresso machines use the rotary or vibration pump. A vibration model makes use of the vibrating disk to create pressure, whereas a rotary model pushes hot water through the ground at a high speed. Both machines can produce excellent espresso but rotary machines are quieter, more durable and less likely to fail.
The Boiler
The boiler is used to heat the water to the perfect temperature to extract. The resulting steam reaches the portafilter which holds ground espresso beans and gets funnelled down into the cup. During this process, steam creates pressure and pushes through the coffee grounds. This produces a layer of crema on top. This is a hallmark of a good espresso.
There are three kinds of espresso machines, each with a different type of pump and brew temperature. There are a variety of ways to control the brew as well as the size of cup that can be produced by the machine.
The earliest espresso machines were steam-based. They utilized one boiler to create both steam and brew however, the pressure they could generate was low - only two bars of atmospheric pressure at most. This resulted in the coffee tasting burnt and bitter. The modern espresso machine was developed by the Milanese manufacturers Luigi Bezzerra & Desiderio Pavoni.
The most commonly used espresso maker is a semi-automatic one with an electric pump. When people think of espresso machines, they think of these machines. Semi-automatic machines require you to grind and tamp your beans yourself however the pump controls the water flow and pressure. This is an excellent solution that combines human control with mechanized accuracy.
The Filter
Typically, espresso machines have filters that separate the grounds of coffee when they pass through the hot water. The filter is also a vital part of the temperature control system, as it keeps the machine from overheating.
It also enhances flavor, since a filter allows for a longer bloom time. This lets the beans release their flavor and improves extraction.
However, it is important to keep in mind that even a top filter can result in a poor cup of coffee, as the quality of the beans and extraction is essential.
This is where the magic happens, it's the thing that makes an espresso really taste good. The grouphead (also called the brewhead) is where you place the portafilter, the thingy used to place the grounds of your coffee into when making espresso.
In a steam-driven espresso machine, hot water is heated in an airtight tank to create steam. Steam is then pushed through the grounds with high pressure. These machines are cheaper and easier for the user to maintain than pumps-driven models. They are however limited in their ability for creating the ideal conditions for brewing as they only operate with 1-1.5 bar of pressure. The ideal shot requires 9-10 bars.
In recent years, compressed air-driven espresso machines have been gaining popularity. They use an air-compressor to force hot water through the ground and are much more mobile than steam-driven electric espresso machines.