How Does Machine Espresso Work?
The machine espresso utilizes precision pressure, and filter technology that is awe-inspiring to make the coffee you enjoy. But how exactly does espresso coffee machine work?
Espresso is produced by pushing hot water 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
The group head is the portafilter that you place in the espresso maker when making it. It distributes water into the portafilter, and then controls the pressure of the extraction. There are numerous kinds of group heads each with distinct advantages and disadvantages. Some are focused on temperature stability, whereas others on pre-infusion options, and others are designed to control the lever. Some have a combination, such as the E61. This is a preferred choice for baristas since it provides multiple advantages in one package.
As you can see in the above image the group head comes with many notches in which you can place your portafilter before twisting it by hand to secure it. There is also a gasket made from rubber which is located inside the notches and helps create an airtight seal after inserting your portafilter into the machine. The notches permit precise placement of your portafilter. This is crucial for a consistent extraction.
The group head does not just allow you to place your portafilter easily but also maintains an even temperature. This is accomplished by cycling hot water around the portafilter and through the brew-basket, ensuring that the temperature is at the right level to extract the coffee. This is important because even a small difference in temperature can be the difference between a good and excellent espresso.
The Pump
Contrary to manual piston machines which use a lever to pressurize water, Rotary espresso machines rely on motorized pumps to deliver the nine atmospheric bars of pressure needed to extract espresso. This pressure builds up by drawing tap water from a reservoir, and pumping it through a heat exchanger prior to being pumped through the ground coffee inside the group head.
Pumps are typically less expensive than piston-driven models, and they tend to last longer, but both types of machines can be damaged by excessive use and inadequate cleaning. They also add mechanical complexity which can result in an expensive price for even the simplest models.
Some espresso machines do away with the pump completely and use steam pressure to brew espresso. The drawback of this is that the boiler that produces steam also increases the temperature of the water to boiling which can cause excessive extraction. In addition these machines typically have to rebuild their pressure between cups, which takes time and energy.
A majority of espresso machines utilize a rotary or vibration pump. A vibration model makes use of a rotating disk to generate pressure, whereas the rotating model pushes hot water through the ground at a fast speed. Both models are capable of producing excellent espresso, however the rotary models are quieter and more durable than vibration pumps.
The Boiler
The boiler heats the water to a temperature that is ideal for extraction. The steam created reaches the portafilter, which contains the espresso coffee grounds. The steam is then channeled into the cup. During this process, steam creates pressure and pushes through the coffee grounds. This results in a crema on the top of the espresso. This is one of the main characteristics of a great espresso.
There are three kinds of espresso machines, each having different types of pumps and the temperature of the brew. There are a variety of ways to control the strength of the brew and the size of the cup that can be made by the machine.
The first espresso machines were steam-based. They utilized a single boiler to make both steam and brew, however the pressure they were able to produce was very low - just two bars of atmospheric pressure, at most. This resulted in the coffee tasting bitter and burnt. The modern espresso machine was created by the Milanese manufacturers Luigi Bezzerra & Desiderio Pavoni.
The most popular espresso machine is a semiautomatic that has an electric pump. When people think of espresso machines, they imagine these machines. With a semi-automatic machine, you need to grind the beans and tamp them by hand. However, the pump controls the flow of water and pressure. This is a great compromise between the human touch and the mechanised consistency.
The Filter
Espresso machines usually have filters that separate the coffee grounds from the hot water. The filter is also an essential element of the temperature control system as it keeps the machine from overheating.
A filter also helps with flavor, as it permits a longer flowering period. This lets the beans release their nuances, and improves extraction.
It is important to remember 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. It's what makes an espresso really taste great. The grouphead, sometimes called the brewhead, is where the portafilter (the container you place the coffee grounds into) sits when you're making espresso.
In the steam-driven espresso machine hot water is heated in an airtight tank to create steam, which is then pushed through the grounds under high pressure. These kinds of machines tend to be less expensive and easier to maintain than pump-driven models. They are however limited for creating the ideal conditions for brewing since they only operate with 1-1.5 bar of pressure. The perfect shot requires 9-10 bars.
In recent years, compressed air-driven espresso machines have become more popular. They utilize an air compressor to force hot water into the grounds and are significantly more portable than steam-driven electric machines.