How Does Machine Espresso Work?
Machine espresso employs precise pressure and incredible filter technology to produce the coffee we love. How exactly does it work?
Espresso is made by pushing hot water under high 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
The group head is the portafilter that you put in when making espresso. It is responsible for dispersing the water into the portafilter before controlling the pressure of the extraction. There are many different types of group heads each with their own advantages and drawbacks. Some focus on temperature stability, 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 favorite among baristas as it provides a variety of advantages in a single package.
As you can see in the above photo, the group head has many notches in which you can put your portafilter, then twist it with your hands to lock it in. There is also a gasket made from rubber 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 crucial for a consistent extraction.
The group head does not just allow you to place your portafilter easily however it also keeps a constant temperature. It does this by circulating hot water through the brew basket, and around the portafilter, ensuring that it is always at the right temperature to extract. It is important to realize that even a slight variation can mean the difference between a great and a great espresso.
The Pump
The motorized pumps used in espresso machines rotary provide nine atmospheric bar pressure required to extract espresso. This differs from manual piston machines which use a lever. This pressure builds up by drawing tap water from a reservoir, and pumping it through a heat exchanger prior being pushed through the ground coffee inside the group head.
Pumps are generally less expensive than piston-driven machines, and tend to last longer. However, both types of machine can be damaged by excessive use and inadequate cleaning. They also create mechanical complexity, which can result in an expensive price for even the simplest models.
Some espresso machines do away with the pump entirely and make use of steam pressure to make espresso. The drawback is that the same boiler that produces steam also increases the temperature of the water to boiling which can cause over-extraction. They also have to continually rebuild their pressure between cups. This takes energy and time.
A majority of espresso machines utilize the rotary or vibration pump. A vibration model employs a vibrating disk to generate pressure, whereas a rotating model pushes hot water through the ground at a rapid speed. Both machines can make great espresso, however rotary machines are quieter, more durable and less likely to break.
The Boiler
The boiler is what is used to heat the water to the perfect temperature for extraction. The steam that is created reaches the portafilter, which contains the espresso coffee grounds. The steam is then channeled into the cup. During this process the steam causes enough pressure to push the grounds of the coffee through. This results in a whipped-up top of the espresso. This is a hallmark of a great espresso.
There are three different types of espresso machines, each having different types of pumps and brew temperature. There are different ways to control the brew as well as the size of cup that can be made by the machine.
The earliest espresso machines were steam-based. The first espresso machines were steam-type machines. This resulted in the coffee tasting espresso and filter coffee machine bitter and burnt. This is why Milanese manufacturers Luigi Bezzerra and Desiderio Pavoni developed the modern espresso machine.
The most popular espresso machine is a semiautomatic 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 on your own while the pump controls the water flow and pressure. This is a perfect compromise between human control and mechanized accuracy.
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 component of the machine's temp control, since it stops overheating.
A filter also helps with flavor, as it permits the beans to flower for a longer period of time. This lets the beans release their nuances, and allows for better extraction.
It is important to keep in mind that even the finest filter can result in a bad cup of coffee. The quality of the beans as well as the extraction, are still very important.
It's in this area that the magic takes place. This is the reason why espresso tastes so good. The grouphead (also called the brewhead) is where you place the portafilter, the thingy which you put the coffee grounds into, when making espresso.
In the steam-driven espresso machine hot water is heated in an airtight container to create steam. This then pushes the hot water through the grounds at a high pressure. These machines are less expensive and easier for the owner to maintain than pumps-driven models. However, they are limited in their ability to produce the perfect brewing conditions because they operate at 1-1.5 bars of pressure. While the perfect shot requires 9-10 bars.
In recent years, espresso machines driven by compressed air-pump have become increasingly popular. They use an air compressor to push hot water through the grounds and are more portable than electric steam-driven machines.