How Does Machine Espresso Work?
The machine espresso is made using precision pressure, and a filter technology that is awe-inspiring to make the coffee you enjoy. But 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 primary difference.
The Group Head
As the name suggests, the group head is where you put your portafilter in when brewing espresso. It is responsible for dispersing the water into the portafilter and controlling the pressure that results from the extraction. There are several different types of group head each with its distinct advantages and disadvantages. Some are focused on temperature stability, while others on pre-infusion features, and others are designed to control the lever. Some come with a combination of both, such as the E61. This is a very popular choice for baristas since it provides multiple benefits in a single package.
As you can see in the photo above, the group head is fitted with several notches. It is possible to place your portafilter into these notches and twist the head 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 allow for precise placement of your portafilter. This is essential for an even extraction.
The group head is not just able to allow you to insert your portafilter easily, but it also maintains the temperature at a constant level. It does this by cycling hot water through the brew basket and around the portafilter, ensuring that it's always at the correct temperature to extract. This is vital, because just a few degrees could make the difference between a excellent and great espresso.
The Pump
Unlike manual piston machines, which rely on a lever that pressurize water, the rotary espresso machines use motorized pumps to deliver the nine atmospheric bars of pressure necessary to extract espresso. The pressure is built by pumping water through a heat-exchanger and then through the ground coffee.
barista espresso coffee machine tend to be cheaper and last longer than piston-driven machines. However, both kinds of machines may degrade due to excessive use and insufficient cleaning. They also make mechanically complex and can lead to costly prices for even the simplest models.
Some espresso machines do away with the pump completely and instead make use of steam pressure to make espresso. The drawback is that the boiler that produces steam also raises the temperature of the water until it reaches boiling which can cause excessive extraction. In addition these machines typically have to rebuild their pressure between cups, which takes time and energy.
Many espresso machines make use of an rotary or a vibration pump. A vibration model makes use of the vibrating disk to create pressure, whereas a Rotary model pushes hot coffee through the ground at a fast speed. Both types of machines can make a great espresso, but the rotary pumps are quieter, and more durable than vibration pumps.
The Boiler
The boiler is the component which heats the water to the ideal temperature to extract. The resulting steam is then transferred to the portafilter, which contains the ground espresso coffee and is then pumped down into the cup. The steam causes enough pressure to push the grounds of coffee through. This creates a crema on the top of the espresso. This is the hallmark of a good espresso.
There are three types of espresso makers. They differ in the type of pump they employ and the degree of heat that the coffee is. There are different ways to control the brew as well as the size of cup that can be made by the machine.
The first espresso machines were steam type. They employed only one boiler to make both steam and brew however the pressure they were able to produce was not very high - two bars of atmospheric pressure at most. The coffee tasted bitter and burnt. This is why Milanese producers Luigi Bezzerra and Desiderio Pavoni invented the modern espresso machine.
The most commonly used espresso maker is a semi-automatic machine that has an electric pump. This is what people envision when they imagine an espresso machine. Semi-automatic machines require you to grind and tamp the beans by yourself The pump, however, regulates the flow of water and pressure. This is a great compromise between human control and mechanized reliability.
The Filter
Typically, espresso machines utilize filters to separate the grounds of the coffee as they go through the hot water. The filter is also an essential part of the machine's temperature control, as it prevents overheating.
A filter also improves flavor because it allows for an extended flowering time. This helps the beans let their nuances out and provides an opportunity for better extraction.
However, it is important to keep in mind that even a great filter can result in a poor cup of coffee, as the quality of the beans and extraction are vital.
This is where the magic happens, it's what makes espresso taste good. The grouphead (also called the brewhead) is where you place the portafilter, which is the thingy used to place 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. This then pushes the hot water through the grounds under high pressure. These types of machines tend to be less expensive and simpler to maintain than pumps-driven models. However, they are limited in their ability to provide the perfect brewing conditions as they only operate at 1-1.5 bars of pressure, while the perfect shot requires 9-10 bars.
In recent times, espresso machines powered by compressed air-pump are becoming increasingly popular. They use an air compressor to force hot water through the ground and are much more mobile than electric steam-driven espresso machines.