How Does Machine Espresso Work?
The machine espresso makes use of precision pressure, and filtering technology that is amazing to make the coffee you 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 pressure is the main difference.
The Head of the Group
The group head is the portafilter that you insert when brewing espresso. It distributes water into the portafilter, and then regulates the pressure of extraction. There are a variety of types of group heads, each with their distinct advantages and disadvantages. Some focus on temperature stability, whereas 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 very popular choice for baristas as it provides a variety of benefits in a single package.
As you can see from the above photo the head of the group is fitted with a variety of notches. You place your portafilter inside these notches, and then twist the head to lock it. There is also a gasket made of rubber which is located inside the notches, which helps create an airtight seal after inserting your portafilter into the machine. The notches permit an exact placement of the portafilter. This is vital for an efficient extraction.
The group head is not just able to allow you to put in your portafilter easily, but it also maintains the same temperature. It does this by circulating hot water through the brew pan and around the portafilter to ensure that it is always at the right temperature for extraction. It is important to note that even a small variation can mean the difference between a great and a excellent espresso.
The Pump
The motorized pumps used in rotary espresso machines supply the nine atmospheric bars of pressure required for espresso extraction. This differs from manual piston machines that use a lever. The pressure builds up by removing tap water from a reservoir and pumping it through a heat exchanger prior to being shot through the ground coffee inside the group head.
Pumps tend to be less expensive than piston-driven machines, and they tend to last longer, but both types of machines could get damaged through overuse and lack of cleaning. Pumps are also more complicated mechanically, which can raise the cost of even most basic models.
Some espresso machines make use of steam pressure instead of a pump to make espresso. This can lead to over-extraction as the boiler that produces steam also heats the water to boil. The machines also need to constantly rebuild their pressure in between here cups. This takes energy and time.
A majority of espresso machines use the rotary or vibration pump, with a vibration model that uses a vibrating disc to create the pressure and a rotary model pushing hot water through the grounds at high speed. Both machines produce great espresso, however rotary machines are more quiet, durable and less likely to break down.
The Boiler
The boiler is the element which heats the water to the ideal temperature for extraction. The steam produced is then directed to the portafilter, which is the container that holds the espresso coffee grounds. It is then funneled into the cup. During this process, the steam creates pressure and pushes through the grounds of the coffee. This creates a layer crema that is then poured over. This is a sign of a great espresso.
There are three distinct types of espresso machines, each with a different type of pump and brew temperature. There are different ways in which the brew can be controlled and the size of the cup that the machine is capable of making.
The first espresso machines were steam type. They utilized only one boiler to make both 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. This is the reason why Milanese producers Luigi Bezzerra and Desiderio Pavoni invented the modern espresso machine.
The most common espresso machine is a semiautomatic one with an electric pump. When people think of espresso machines, they think of these machines. With a semi-automatic espresso machine, you grind the beans and then tamp them by hand, but the pump regulates the flow of water and pressure. This is a fantastic compromise between human control and mechanized reliability.
The Filter
Typically, espresso machines use filters to separate the grounds of coffee as they move through the hot water. The filter is also an essential part of the temperature control system, as it keeps the machine from overheating.
It also aids in flavor, as it allows for a longer bloom phase. This allows the beans to release their flavor and allows for a better extraction.
However, it is important to remember that even a high-quality filter could result in a bad cup of coffee, because the quality of the beans and extraction is crucial.
It's in this area that the magic occurs. This is the reason why espresso tastes so delicious. The grouphead, also called the brew head, is where the portafilter (the container you place the coffee ground into) is placed when making espresso.
Steam-driven espresso machines use hot water heated in an airtight container to create steam. The steam then pushes hot water into the grounds of coffee at high pressure. These types of machines are typically less expensive and simpler to maintain than pump-driven models. However, they are limited in their ability to create the ideal brewing conditions, because they operate at 1-1.5 bars of pressure, while the perfect shot requires 9-10 bars.
In recent years, compressed air-pump-driven espresso machines have been gaining popularity. They use an air-compressor to force hot water through the ground, and are more mobile than electric steam-driven espresso machines.