How Does Machine Espresso Work?
Machine espresso makes use of precise pressure and incredible filter technology to produce the coffee we love. How does it work exactly?
Espresso is created by forcing hot water at high pressure through finely ground coffee. The process is similar to that of making drip coffee. However, the pressure is the major difference.
The Head of the Group
As the name suggests the group head is the place you put your portafilter in when brewing espresso. It is responsible for dispersing water into the portafilter, and controlling the pressure of the resulting extraction. There are several different types of group heads each with its distinct advantages and drawbacks. Some focus on temperature stability, while others on pre-infusion options, and others are designed to control the lever. Some come with a combination of both, like the E61. This is a favorite among baristas because it offers multiple advantages in a single package.
As you can see in the above photo The group head features several notches where you put your portafilter, then twist it with your hands to secure it. There is also a gasket made from rubber which is located inside the notches to help create an airtight seal after inserting your portafilter into the machine. The notches on the head permit an exact location of the portafilter which is vital to ensure an even extraction.
The group head not only lets you to place your portafilter easily but also maintains an even temperature. It does this by circulating hot water through the brew pan and around the portafilter, ensuring that it's always at the correct temperature for extraction. This is important, as just a few degrees could mean the difference between good and great espresso.
The Pump
The motorized pumps that are used in espresso machines that rotate provide the nine atmospheric bar pressure needed to extract espresso. This differs from manual piston machines that rely on a lever. The 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 in the group head.
Pumps tend to be cheaper and last longer than piston-driven machines. However, both kinds of machines can degrade due to overuse and insufficient cleaning. Pumps are also more complicated mechanically, which can increase prices of even most basic models.
Some espresso machines make use of steam pressure instead of a pump in order to brew espresso. This can lead to over-extraction as the boiler that makes steam also warms the water to boil. Additionally these machines typically have to restore their pressure between cups, which requires time and energy.
A majority of espresso machines utilize either a vibration or rotary pump. A vibration model employs a vibrating disk to generate pressure, while the rotary model pushes hot water through the ground at a fast speed. Both models can make a great espresso, however the rotary pumps are quieter, and more durable than vibration pumps.
The Boiler
The boiler is the part that heats the water to the optimal temperature for extraction. The resultant steam then reaches the portafilter containing the ground espresso and is then funneled down into the cup. The steam creates enough pressure to push the grounds of the coffee through. This results in a layer of crema that is then poured over. This is one of the main characteristics of a great espresso.
There are three types of espresso makers. They differ in the kind of pump they use and the degree of heat that the brew is. There are different ways that the brew may be controlled as well as the size of the cup that the maker can create.
The first espresso machines were steam-type. They used a single boiler to make steam and brew, however, the pressure they could generate was low - only two bars of atmospheric pressure at most. The coffee tasted bitter and burned. This is why Milanese manufacturers 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. If you have a semi-automatic machine you grind the beans and then tamp them yourself but the pump controls the flow of water and pressure. This is an excellent compromise between human touch and the mechanized quality.
The Filter
Typically, espresso machines employ a filter to separate out the grounds of coffee when they pass through the hot water. The filter is also a vital part of the temperature control system, as it keeps the machine from overheating.
A filter also helps with flavor since it allows for a longer flowering phase. espresso coffee machine for home allows the beans to let their nuances out and provides an opportunity for better extraction.
However it is crucial to remember that even a great filter can result in a poor cup of coffee, because the quality of the beans and extraction is important.
It's in this area that the magic occurs. This is what makes espresso taste so delicious. The grouphead, also referred to as the brewhead, is where the portafilter (the container you place the coffee grounds into) is placed when making espresso.
Steam-driven espresso machines make use of hot water that is heated inside an airtight container to create steam. The steam then pushes hot water into the grounds of coffee at high pressure. These machines are less expensive and easier for the user to maintain than pumps-driven models. They are however limited for creating the ideal conditions for brewing as they only operate with 1-1.5 bar of pressure. The ideal shot requires 9-10 bars.
In recent times, espresso machines powered by a compressed air compressor have become increasingly popular. They utilize an air compressor to force hot water through grounds and are significantly more portable than steam-driven electric machines.