How Does Machine Espresso Work?
Machine espresso utilizes precise pressure and mind-blowing filter technology to make the perfect cup of coffee. How exactly does it work?
Espresso is made by pushing hot water under high pressure through finely ground coffee. The process is similar to making drip coffee but the key difference is in the pressure.
The Head of the Group
The group head is the portafilter that you place in the espresso maker when making it. It disperses water in the portafilter and regulates the pressure during the extraction. There are numerous kinds of group heads each with distinct advantages and disadvantages. Some are designed for temperature stability while others are built to handle pre-infusion. Others are made to control the lever. Some are a combination, like the E61. This is a popular choice among baristas because it offers multiple benefits in a single package.
As you can see in the photo above the group head is made up of numerous notches that you can put your portafilter, then twist it by hand to secure it. A gasket made of rubber is positioned in the notches to make a seal when you insert your portafilter. The notches on the head permit an exact placement of the portafilter, which is crucial to ensure an even extraction.
The group head not only lets you to place your portafilter easily however it also keeps the temperature at a constant level. This is accomplished by cycling hot water around the portafilter, and through the brew-basket to ensure that the temperature is at the right level to extract the coffee. It is crucial to keep in mind that even a tiny variation can mean the difference between a good and excellent espresso.
The Pump
Motorized pumps in rotary espresso machines provide the nine atmospheric bar pressure that is required for espresso extraction. This differs from manual piston machines which use a lever. This pressure is built up by pumping water through a heat-exchanger and then through the ground coffee.
Pumps are typically less expensive and last longer than piston-driven machines. However, both kinds of machines can deteriorate due to overuse and inadequate cleaning. Pumps are also more complicated mechanically, which can raise prices of even simple models.
Some espresso machines eliminate the pump completely and instead make use of steam pressure to make espresso. This could lead to over-extraction since the boiler that produces steam also causes the water to boil. Additionally these machines typically have to rebuild their pressure between cups, which requires time and energy.
A large majority of espresso machines employ the rotary or vibration pump. A vibration model makes use of a rotating disk to generate pressure, while the rotating model pushes hot water through the ground at a fast speed. Both machines can make excellent espresso, but rotary machines are more quiet, durable and less likely to fail.
The Boiler
The boiler makes the water warm to the ideal temperature for extraction. The steam produced gets to the portafilter which holds the espresso grounds. It is then poured into the cup. During this process the steam creates enough pressure to push the grounds of the coffee through. This produces a layer of crema on top. This is a sign of a good espresso.
There are three types of espresso makers, and they differ in the type of pump they use and the degree of heat that the coffee is. There are also different ways that the brew can be controlled, as well as the size of the cup the machine can produce.
The first espresso machines were steam-type. They utilized one boiler to make both steam and brew, but the pressure they could produce was not very high - two bars of atmospheric pressure, at most. The coffee tasted bitter and burned. This is the reason why Milanese producers Luigi Bezzerra and Desiderio Pavoni invented the modern espresso machine.
The most commonly used espresso maker is a semi-automatic one that has an electric pump. When people think of espresso machines, they think of these machines. With a semi-automatic machine, you must grind the beans and tamp them by hand, but the pump regulates the flow of water and pressure. This is an excellent combination of human control and mechanized reliability.
The Filter
Typically, espresso machines employ filters that separate the coffee grounds as they pass through the hot water. The filter is also a vital part of the machine's temperature control, as it prevents overheating.
Filters also aid in flavor as it allows for an extended flowering time. This helps the beans let their nuances out and provides the chance for better extraction.
However, it is important to remember that even a high-quality filter can produce a bad cup of coffee, because the quality of the beans and extraction are essential.
It's in this area that the magic happens. This is the reason why espresso tastes so delicious. The grouphead, sometimes called the brewhead, is where the portafilter (the device you put the coffee grounds into) is placed when making espresso.
In a steam-driven espresso machine, hot water is heated in an airtight tank to create steam. espresso machines uk pushes the hot water through the grounds at high pressure. These types of machines tend to be less expensive and simpler to maintain than pump-driven models. They are however limited in their ability 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 compressed air-pump have become increasingly popular. They use an air compressor to force hot water through grounds, and are far more portable than steam-driven electric machines.