How Does Machine Espresso Work?
Machine espresso employs precise pressure and amazing filter technology to make the perfect cup of coffee. 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, but the key difference is in the pressure.
The Group Head
The group head is the portafilter that you place in the espresso maker when making it. It is responsible for dispersing water into the portafilter before controlling the pressure of the resulting extraction. There are many different types of group heads each with distinct advantages and disadvantages. Some are designed to provide temperature stability while others are built to handle pre-infusion. Others are built to control the lever. Some come with a combination of both, such as the E61. This is a very popular choice for baristas due to the fact that it has multiple benefits in a single package.
As you can see in the image above the group head is made up of many notches in which you can place your portafilter and then twist it manually to secure it. There is also a rubber gasket which is located inside the notches and helps to create an airtight seal after inserting your portafilter into the machine. The notches permit an exact placement of the portafilter. This is essential for an efficient extraction.
The group head does not just allow you to insert your portafilter easily however, it also keeps the same temperature. It does this by circulating hot water through the brew basket and around the portafilter, making sure that it is always at the right temperature to extract. This is vital, because even a few degrees can mean the difference between good and excellent espresso.
The Pump
The motorized pumps used in rotary espresso machines provide the nine atmospheric bar pressure that is required to extract espresso. 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 tend to be more affordable and last longer than piston-driven machines. However, both types of machines can degrade due to overuse and insufficient cleaning. Pumps are also more complicated mechanically, which could increase the cost of even most basic models.
Certain espresso machines utilize steam pressure instead of a pump to make espresso. This could lead to over-extraction since the boiler that makes steam also heats the water to boil. These machines 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 an oscillating disk to create pressure, whereas a rotating model pushes hot water through the ground at a rapid speed. Both machines can produce excellent espresso, but rotary machines are more stable, quieter and less likely to break.
The Boiler
The boiler is the part that heats water to the ideal temperature to extract. The steam produced reaches the portafilter, which is the container that holds the espresso coffee grounds. It is then pumped into the cup. During this process, the steam creates pressure to push through the grounds of the coffee. This results in a layer of crema that is then poured over. This is a sign of a good espresso.
There are three distinct types of espresso machines, each having different pumps and brew temperature. There are different ways to control the brew and the size of the cup that can be produced by the machine.
The first espresso machines were steam-type. They employed one boiler to make both steam and brew however, the pressure they could produce was not very high - two bars of atmospheric pressure at most. This resulted in the coffee tasting burnt and bitter. The modern espresso machine click here was created by the Milanese producers Luigi Bezzerra & Desiderio Pavoni.
The most common espresso machine is a semiautomatic one with an electric pump. These are what people imagine when they think of an espresso machine. With a semi-automatic espresso machine, you have to grind the beans and then tamp them by hand, but the pump is able to regulate the flow of water and pressure. This is a great compromise between the human touch and the mechanised quality.
The Filter
Espresso machines typically use filters that separate the grounds of coffee from hot water. The filter is also a vital part of the machine's temperature control, as it prevents overheating.
It also aids in flavor, as it allows for a more prolonged bloom time. This allows beans to release their flavor and gives an opportunity for a better extraction.
It is important to keep in mind that even the best filter can produce a bad cup of coffee. The quality of the beans and the extraction process remain vital.
It's here that the magic happens. This is what makes espresso taste so delicious. The grouphead (also called the brewhead) is where you place the portafilter, the device used to place the coffee grounds into, while making espresso.
In a steam-driven espresso machine hot water is heated in an airtight container to create steam, which is then pushed through the grounds at a high pressure. They are less expensive and are easier for the user to maintain than pumps-driven models. They are however limited for creating the ideal 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-driven espresso machines have become more popular. They use an air-compressor to force hot water through the ground and are much more mobile than electric steam-driven espresso machines.