How Does Machine Espresso Work?
Machine espresso employs precise pressure and mind-blowing filter technology to make the coffee we love. But how exactly does it work?
Espresso is created by forcing hot water at high pressure through finely ground coffee. The process is similar to making drip coffee, however the main difference lies in the pressure.
The Group Head
The group head is the portafilter that you put in when making espresso. It distributes water into the portafilter, and regulates the pressure of extraction. There are many different kinds of group heads, each with their own advantages and drawbacks. Some are designed to provide the stability of temperature while some are designed to handle pre-infusion. Others are made to control the lever. There are even some that come with a range of features, such as the E61, which is considered the most popular choice among baristas due to its capacity to offer multiple benefits in a single package.
As you can see in the photo above the group head is made up of several notches to place your portafilter before twisting it by hand to lock it in. A gasket made of rubber is placed within the notches to make a seal when you insert your portafilter. The notches on the head permit an exact position of the portafilter which is crucial to ensure a consistent extraction.
The group head not only lets the portafilter to be inserted easily but also maintains the temperature at a constant level. It does this by cycling hot water through the brew pan and around the portafilter, making sure that it's always at the correct temperature for extraction. This is vital, because even a small difference in temperature can make the difference between good and great espresso.
The Pump
In contrast to piston machines that are manually operated, which rely on a lever that pressurize water, rotary espresso machines rely on motorized pumps to provide the nine atmospheric bars of pressure required for espresso extraction. This pressure is generated by pumping water through a heat exchanger and then through the ground coffee.
Pumps tend to be less expensive and last for longer than piston-driven machines. However, both kinds of machines may degrade due to overuse and poor cleaning. Pumps are also more complicated mechanically, which could increase the cost of even the most basic models.
Certain espresso machines remove the pump completely and instead employ steam pressure to create espresso. This could lead to over-extraction since the boiler that produces steam also heats the water to boil. Additionally these machines are often required to rebuild their pressure between cups, which takes time and energy.
Many espresso machines employ the rotary or vibration pump, with a vibration model using a vibrating disc to create the pressure and an rotary model that espresso machines pushes hot water through the grounds under high speed. Both machines can produce excellent espresso but rotary machines are more stable, quieter and less likely to fail.
The Boiler
The boiler is the part that heats water to the ideal temperature to extract. The steam produced is then directed to the portafilter, which contains the espresso coffee grounds. It is then pumped into the cup. In this process, the steam creates pressure to push through the coffee grounds. This produces a layer of crema on top. This is one of the main characteristics of a great espresso.
There are three kinds of espresso makers, and they differ in the kind of pump they use and the degree of heat that the brew is. There are a variety of ways to control the amount of brew, as well as the size of the cup that can be produced by the machine.
The first espresso machines were steam-type. They employed one boiler to create both steam and brew, however, the pressure they could produce was very low - just two bars of atmospheric pressure at most. The coffee tasted bitter and burnt. This is why the Milanese makers Luigi Bezzerra and Desiderio Pavoni developed the modern espresso machine.
The most well-known espresso maker is a semi-automatic machine 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 while the pump controls the water flow and pressure. This is an excellent compromise between human touch and mechanized consistency.
The Filter
Typically, espresso machines employ a filter to separate out the grounds of the coffee as they go through the hot water. The filter is also an essential element of the machine's temperature control, as it prevents overheating.
It also helps with flavor, as a filter allows for a more prolonged bloom time. This helps the beans to let their nuances out and provides the chance for better extraction.
It is important to keep in mind that even the finest filter can produce a bad cup of coffee. The quality of the beans and the extraction process remain crucial.
This is where the magic happens, it's the thing that makes an espresso really taste great. The grouphead (also called the brewhead) is where you put the portafilter - the thingy that you use to put the grounds of your coffee into while making espresso.
In a steam-driven espresso machine hot water is heated in an airtight tank to create steam, which then pushes the hot water through the grounds under high pressure. These types of machines tend to be cheaper and easier to maintain than pump-driven models. They are however limited to create the perfect conditions for brewing, as they operate with 1-1.5 bar of pressure. The perfect shot requires 9-10 bars.
In recent years, espresso machines powered by a compressed air compressor have become increasingly popular. They use an air compressor to push the hot water through the grounds and are significantly more portable than electric steam-driven machines.