How Does Machine Espresso Work?
The machine espresso makes use of precise pressure and filter technology that is mind-blowing to make the coffee you enjoy. How exactly does it work?
In order to make espresso hot water is pushed under pressure through finely ground coffee. The process is similar to making drip coffee. However the pressure is the main difference.
The Head of the Group
As the name implies, the group head is where you insert your portafilter when making espresso. It is responsible for dispersing the water into the portafilter and then controlling the pressure of the resulting extraction. There are various kinds of group heads, each with their unique advantages and disadvantages. Some are focused on temperature stability, while others on pre-infusion features, and others are designed to control the lever. Some are 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 above image the group head is made up of several notches where you place your portafilter and then twist it with your hands to lock it in. A gasket made of rubber is positioned in the notches to create a seal when you insert your portafilter. The notches on the head permit an exact placement of the portafilter, which is necessary for a consistent extraction.
Apart from allowing you easily place your portafilter in, the group head is responsible to maintain an even temperature. This is accomplished by cycling hot water around the portafilter and through the brew-basket, making sure that the temperature is always at the right level for extraction. This is important because even a small difference in temperature can mean the difference between good and excellent espresso.
The Pump
In contrast to manual piston machines which rely on a lever to pressurize water, the rotary espresso machines use motorized pumps to provide the nine atmospheric bars of pressure necessary for espresso extraction. The pressure is created by pumping water through a heat exchanger and then through the ground coffee.
Pumps are typically less expensive and last for longer than piston-driven machines. However, look here of machines are susceptible to degrading because of frequent use and inadequate cleaning. Pumps are also more complicated mechanically, which can increase the price of even the simplest models.
Some espresso machines eliminate the pump entirely and utilize steam pressure to make espresso. The drawback is that the boiler that produces steam also raises the temperature of the water to boiling and can result in over-extraction. In addition the machines often have to rebuild their pressure between cups, which requires time and energy.
Many espresso machines employ either a rotary or vibration pump, with a vibrating model that uses a vibrating disc to create pressure and the rotary model pushing hot water through the grounds under high speed. Both machines can make great espresso however rotary machines tend to be more stable, quieter and less likely to break down.
The Boiler
The boiler is the component that heats the water to the ideal temperature for extraction. The steam that is produced gets to the portafilter which is the container that holds the espresso coffee grounds. It is then pumped into the cup. The steam creates pressure that pushes 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 distinct types of espresso machines, each with a different type of pump and the temperature of the brew. There are a variety of ways to control the brew as well as the size of the cup that can be made by the machine.
The earliest espresso machines were steam types. They employed only one boiler to make both brew and steam, however the pressure they were able to produce was very low - just two bars of atmospheric pressure maximum. This led to the coffee tasting burnt and bitter. This is why Milanese makers Luigi Bezzerra and Desiderio Pavoni developed the modern espresso machine.
The most common espresso machine is a semiautomatic model with an electric pump. These are the things people think of when they think of an espresso maker. With a semi-automatic machine you grind the beans and tamp them yourself but the pump controls the flow of water and pressure. This is an excellent compromise between human touch and the mechanized consistency.
The Filter
Espresso machines typically have filters that separate the grounds of coffee from hot water. The filter is also an essential part of the temperature control system, since it helps prevent the machine from overheating.
It also helps with flavor, as it can allow for a longer bloom time. This helps the beans release their flavors and provides an opportunity to improve extraction.
However it is crucial to remember that even a top filter can result in a poor cup of coffee, since the quality of the beans and extraction are important.
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 which you put the grounds of coffee into when making espresso.
In a steam-driven espresso machine hot water is heated in an airtight container to create steam. Steam then pushes the hot water through the grounds under high pressure. They are less expensive and easier for the owner to maintain than pumps-driven models. However, they are not as efficient in their ability to provide the perfect brewing conditions since they operate at 1-1.5 bars of pressure, while the perfect shot requires 9-10 bar.
In recent years, espresso machines driven by compressed air-pump are becoming increasingly popular. They use an air compressor to force hot water into the grounds and are much more portable than electric steam-driven machines.