How Does Machine Espresso Work?
Machine espresso employs precise pressure and mind-blowing filter technology to make the coffee we love. How does it work exactly?
Espresso is created by forcing hot water under 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
As the name implies the group head is the place you insert your portafilter when brewing espresso. It disperses the water into the portafilter, and then regulates the pressure of the extraction. There are many different types of group heads, each with its own advantages and disadvantages. Some are designed to provide temperature stability while others are designed to handle pre-infusion. Others are made to control the lever. Some include a combination 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 from the photo above the group head is fitted with several notches. The portafilter is placed inside these notches, and then twist the head to lock it. There is also a rubber gasket in the notches and helps create the seal when you insert your portafilter into the machine. The notches allow for the precise placement of the portafilter. This is vital for an efficient extraction.
Apart from allowing you easily connect your portafilter, the group head is also responsible for maintaining a consistent temperature. It does this by circulating hot water through the brew container and around the portafilter, ensuring that it's always at the correct temperature for extraction. This is important because even a few degrees can make the difference between good and excellent espresso.
The Pump
The motorized pumps in espresso machines that rotate provide the nine atmospheric bar pressure that is required to extract espresso. This is different from manual piston machines that rely on a lever. This pressure is generated by pumping water through a heat-exchanger and then through the ground coffee.
Pumps are generally less expensive than piston-driven models, and they tend to last longer, but both types of machines could be damaged by excessive use and inadequate cleaning. They also make mechanically complex that can lead to an expensive price for even the simplest models.
Certain espresso machines remove the pump completely and instead make use of steam pressure to make espresso. This can cause over-extraction because the boiler that makes steam also causes the water to boil. The machines also need to constantly rebuild their pressure in between cups. This requires energy and time.
Many espresso machines utilize either a rotary or vibration pump, with a vibrating model using a vibrating disc that generates the pressure, and rotating models that push hot water through the grounds under high speed. Both machines can make excellent espresso, however rotary machines are more stable, quieter and less likely to fail.
The Boiler
The boiler is the component that heats the water to the optimal temperature to extract. The resulting steam reaches the portafilter, which contains ground espresso beans and gets funnelled down into the cup. The steam generates enough pressure to push the coffee grounds through. This results in a layer of crema on top. This is the hallmark of a great espresso.
There are three kinds of espresso makers, which differ in the kind of pump they use and the degree of heat that the espresso is. There are also different ways in which the brew can be controlled, as well as the dimensions of the cup the machine can produce.
The first espresso machines were steam type. They employed one boiler to create both steam and brew, however, the pressure they could produce was not very high - two bars of atmospheric pressure maximum. This resulted in the coffee tasting burnt and bitter. The modern espresso machine was created by the Milanese makers Luigi Bezzerra & Desiderio Pavoni.
The most common espresso machine is a semiautomatic with an electric pump. These are the images people have when they imagine an espresso machine. With a semi-automatic espresso machine, you need to grind the beans and then tamp them by hand. The pump is able to regulate the flow of water and pressure. This is an excellent compromise between human touch and the mechanised accuracy.
The Filter
Espresso machines usually use a filter that separates the grounds of the coffee from the hot water. look here is also a vital component of the machine's temperature control, as it helps prevent overheating.
It also aids in flavor, since a filter lets you enjoy a longer bloom time. This lets the beans release their nuances, and allows for a better extraction.
However, it is important to keep in mind that even a great filter can produce a bad cup of coffee, because the quality of the beans and extraction is still vital.
This is where the magic happens, and it's what makes espresso taste great. The grouphead (also known as the brewhead) is where you place the portafilter, the device that you put the grounds of coffee into when making espresso.
Steam-driven espresso machines use hot water that is heated in an airtight container to make steam. The steam then pushes hot water through the grounds of the coffee under pressure. These machines are less expensive and easier for the owner to maintain than pumps-driven models. However, they are not as efficient in their ability to produce the perfect conditions for brewing, as they only 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 utilize an air compressor to force hot water through the ground and are more mobile than steam-driven electric espresso machines.