How Does Machine Espresso Work?
Machine espresso makes use of precise pressure and amazing filter technology to make the coffee we love. What exactly is it that makes 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 main difference lies in the pressure.
The Head of the Group
The group head is the portafilter that you insert when brewing espresso. It is responsible for dispersing the water into the portafilter before controlling the pressure that results from the extraction. There are a variety of group heads, each with its own advantages and drawbacks. Some are specifically designed for stability of temperature while others are built to handle pre-infusion. Others are made to control the lever. Some are a combination, such as the E61. This is a favorite among baristas because it offers multiple advantages in a single package.
As you can see in the image above The group head features numerous notches that you can put your portafilter, then twist it by hand to lock it in. There is also a gasket made from rubber that resides inside the notches to help create the seal when you insert your portafilter into the machine. The notches permit an exact placement of the portafilter. This is crucial for a consistent extraction.
In addition to allowing you to effortlessly insert your portafilter the group head is responsible for maintaining an even temperature. It does this by circulating hot water through the brew container and around the portafilter, ensuring that it's always at the correct temperature to extract. This is crucial, since even a small difference in temperature can make the difference between excellent and great espresso.
The Pump
In contrast to manual piston machines which rely on a lever that pressurize water, rotating espresso machines rely upon motorized pumps to provide the nine atmospheric bars of pressure that are required to extract espresso. This pressure is built up by pumping water through a heat-exchanger and then through the ground coffee.
Pumps are generally less expensive than piston-driven machines and tend to last longer. However, both types of machines could degrade with overuse and insufficient cleaning. Pumps are also more complex mechanically, which can raise prices of even simple models.
Certain espresso machines eliminate the pump completely and make use of steam pressure to make espresso. This can lead to over-extraction as the boiler that makes steam also heats the water to boil. They also have to constantly rebuild their pressure between cups. This requires energy and time.
Many espresso machines use the rotary or vibration pump. A vibration model uses the vibrating disk to create pressure, whereas a rotating model pushes hot water through the ground at a rapid speed. Both models are capable of producing excellent espresso, but Rotary machines are quieter and more durable than vibration pumps.
The Boiler
The boiler is what heats the water to the ideal temperature to extract. The resulting steam reaches the portafilter containing the ground espresso and is then pumped into the cup. The steam creates enough pressure to push the grounds of coffee through. This creates a crema on top of the espresso. This is a hallmark of a great espresso.
There are three types of espresso machines, each having different types of pumps and the temperature of the brew. There are many ways to control the strength of the brew and the size of the cup that can be made by the machine.
The first espresso italian espresso machine machines were steam-type. They utilized only one boiler to make steam and brew, however the pressure they were able to generate was low - only two bars of atmospheric pressure at the most. The coffee tasted bitter and burnt. The modern espresso machine was developed by the Milanese manufacturers Luigi Bezzerra & Desiderio Pavoni.
The most popular espresso machine is a semiautomatic one with an electric pump. These are what people imagine when they think of an espresso machine. Semi-automatic machines require you to grind and tamp the beans on your own however the pump controls the flow of water and pressure. This is a great combination of human control and mechanized consistency.
The Filter
Typically, espresso machines utilize a filter to separate out the grounds of the coffee as they go through the hot water. The filter is also an essential component of the machine's temp control, as it prevents overheating.
It also helps with flavor as a filter lets you enjoy a longer bloom phase. This helps the beans to release their nuances and gives an opportunity for a better extraction.
However it is crucial to remember that even a high-quality filter can make a terrible cup of coffee, because the quality of the beans and extraction is still vital.
It's in this area that the magic takes place. This is what makes espresso taste so delicious. The grouphead, sometimes referred to as the brewhead, is where the portafilter (the thing you put the ground coffee in) is placed when making espresso.
Steam-driven espresso machines make use of hot water that is heated inside an airtight container to make steam. The steam then pushes hot water through coffee grounds under high pressure. These machines are cheaper and easier for the user to maintain than pumps-driven models. They are however limited to create the perfect conditions for brewing, as they operate with 1-1.5 bar of pressure. The ideal shot requires 9-10 bars.
In recent years, compressed-air-pump-driven espresso machines have become more popular. They use an air compressor to force the hot water through the grounds and are significantly more portable than steam-driven electric machines.