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?
In order to make espresso hot water is pushed under pressure through finely ground coffee. The process is similar to making drip coffee. However it is the pressure that makes the main difference.
The Head of the Group
As the name implies, the group head is where you place your portafilter while brewing espresso. It disperses water in the portafilter, and then controls the pressure of the extraction. There are many different types of group heads each with its own advantages and disadvantages. Some focus on temperature stability, others on pre-infusion options, and others are designed to control the lever. Some are a combination, such as the E61. This is a favorite among baristas due to the fact that it has multiple benefits in one package.
As you can see in the photo above the head of the group is fitted with several notches. The portafilter is placed in these notches and then turn the head around to secure it. A gasket made of rubber is placed inside the notches, which helps create a seal as you insert your portafilter. The notches allow for the precise placement of the portafilter. This is essential for a consistent extraction.
The group head not only allows you to put in your portafilter easily however, it also keeps the temperature at a constant level. It does this by cycling hot water through the brew basket, and around the portafilter to ensure that it is always at the right temperature to extract. This is important, as even a few degrees can mean the difference between good and excellent espresso.
The Pump
Motorized pumps in rotary espresso machines provide the nine atmospheric bar pressure needed to extract espresso. This is different from manual piston machines which use levers. The pressure builds by drawing tap water from a reservoir and pumping it through a heat exchanger prior being pushed through the ground coffee in the group head.
Pumps tend to be less expensive and last for longer than piston-driven machines. However, both types of machines can deteriorate due to overuse and poor cleaning. They also increase the complexity of mechanical systems and can lead to costly prices for even the simplest models.
Some espresso machines can eliminate the pump entirely and use steam pressure to brew espresso. The disadvantage of this is that the same boiler that produces steam also increases the temperature of water until it reaches boiling, which can lead to over-extraction. The machines must also continuously rebuild their pressure between cups. This requires energy and time.
Many espresso machines use either a vibration or rotary pump. A vibration model employs a rotating disk to generate pressure, while the Rotary model pushes hot coffee through the ground at high speed. Both machines can make great espresso but rotary machines are more stable, quieter and less likely to break.
The Boiler
The boiler is used to heat the water to the ideal temperature for extraction. The steam that is produced reaches the portafilter containing ground espresso beans and is then funneled down into the cup. During this process, steam creates pressure that pushes through the coffee grounds. This results in a layer of crema on top. This is a hallmark of a great espresso.
There are three types of espresso machines, each having different types of pumps and brew temperature. There are various ways to control the brew as well as the size of cup that can be produced by the machine.
The first espresso machines were steam-type. The earliest espresso machines were steam-type machines. This led to the coffee tasting burnt and bitter. The modern espresso machine was invented by the Milanese producers Luigi Bezzerra & Desiderio Pavoni.
The most commonly used espresso machine is a semiautomatic model with an electric pump. When people think of espresso machines, they imagine these machines. Semi-automatic machines require you to grind and tamp the beans by yourself, but the pump regulates the flow of water and pressure. This is a perfect combination of human control and mechanised accuracy.
The Filter
Espresso machines typically have filters that separate the grounds of the coffee from hot water. The filter is also an essential element of the temperature control system, because it stops the machine from overheating.
It also improves flavor, as a filter allows for a longer bloom time. This lets the beans let their nuances out, and improves extraction.
It is important to keep in mind that even the finest filter could result in a poor cup of coffee. The quality of the beans and the extraction, remain crucial.
This is where the magic happens, and it's what makes an espresso really taste good. The grouphead, sometimes called the brew head, is the place where the portafilter (the thing you put the ground coffee in) is placed when you're making espresso.
In a steam-driven espresso machine hot water is heated in an airtight coffee machine for home tank to create steam. Steam is then pushed through the grounds at high pressure. These kinds of machines are typically less expensive and simpler to maintain than pump-driven models. However, they are limited in their ability to produce the ideal conditions for brewing since they operate at 1-1.5 bars of pressure. While the perfect shot requires 9-10 bar.
In recent years, espresso machines driven by compressed air-pump are becoming increasingly popular. They use an air compressor to push hot water across the ground, and are more mobile than electric steam-driven espresso machines.