How Does Machine Espresso Work?
Machine espresso utilizes precise pressure and incredible filter technology to produce the delicious coffee we enjoy. What exactly does it work?
In order to make espresso hot water is forced under high pressure through finely ground coffee. The process is similar to making drip coffee but the major difference is in the pressure.
The Head of the Group
The group head is the portafilter you insert when brewing espresso. It is responsible for dispersing water into the portafilter and then controlling the pressure of the resulting extraction. There are a variety of types of group heads each with its unique advantages and drawbacks. Some focus on temperature stability, while others on pre-infusion capabilities, while others are designed to control the lever. Some are a combination, such as the E61. This is a favorite among baristas since it provides multiple advantages in a single package.
As you can see in the above photo the group head is made up of several notches to place your portafilter and twist it manually to lock it in. There is also a gasket made of rubber which is located inside the notches and helps create an airtight seal when you insert your portafilter into the machine. The notches on the head allow for an exact position of the portafilter which is essential for a consistent extraction.
The group head not only lets the portafilter to be inserted easily however it also keeps an even temperature. It does this by circulating hot water through the brew container and around the portafilter, ensuring that it's always at the right temperature to extract. This is crucial, since even a small difference in temperature can mean the difference between good and great espresso.
The Pump
Contrary to manual piston machines which rely on a lever that pressurize water, Rotary espresso machines rely on motorized pumps to supply the nine atmospheric bars of pressure required for espresso extraction. This pressure is generated by pumping water through a heat-exchanger and then through the ground coffee.
Pumps are generally less expensive and last longer than piston-driven machines. However, both types of machines are susceptible to degrading because of excessive use and insufficient cleaning. Pumps are also more complicated mechanically, which can raise prices of even simple models.
Some espresso machines employ steam pressure instead of a pump for brewing espresso. The drawback is that the same boiler that produces steam also raises the temperature of the water to boiling and can result in over-extraction. The machines also need to constantly rebuild their pressure between cups. This requires energy and time.
A majority of espresso machines use an rotary or vibrating pump, which is a vibration model that uses a vibrating disc to create pressure, and a rotary model pushing hot water through the grounds under high speed. Both machines can make excellent espresso but rotary machines are more stable, quieter and less likely to fail.
The Boiler
The boiler is the element that heats water to an ideal temperature to extract. The steam that is produced gets to the portafilter which is the container that holds the espresso coffee grounds. The steam is then channeled into the cup. The steam creates pressure and pushes through the grounds of the coffee. This results in a layer of crema that is then poured over. This is the hallmark of a good espresso.
There are three different types of espresso machines, each having a different type of pump and the temperature of the brew. There are a variety of ways to control the strength of the brew and the size of cup that can be made by the machine.
The earliest espresso machines were steam types. They utilized one boiler to create steam and brew, however, the pressure they could generate was low - only two bars of atmospheric pressure at most. This led to the coffee tasting bitter and burnt. The modern espresso machine was developed by the Milanese makers Luigi Bezzerra & Desiderio Pavoni.
The most well-known espresso maker is a semiautomatic machine with an electric pump. This is what people envision when they think of an espresso machine. coffeee.uk -automatic machines require you to grind and tamp the beans by yourself however the pump controls the flow of water and pressure. This is an excellent compromise between human touch and the mechanized quality.
The Filter
Typically, espresso machines have filters that separate the grounds of the coffee as they go through the hot water. The filter is also a crucial element of the temperature control system as it keeps the machine from overheating.
A filter can also help with flavor as it allows for an extended flowering time. This helps the beans to release their flavors and provides an opportunity for better extraction.
It is important to keep in mind that even the most efficient filter can produce a bad cup of coffee. The quality of the beans, and the extraction, remain vital.
This is where the magic happens, it's the thing that makes espresso taste great. The grouphead (also known as the brewhead) is where you put the portafilter - the thingy that you use to put the coffee grounds into, while making espresso.
In the steam-driven espresso machine hot water is heated in an airtight tank to create steam, which is then pushed through the grounds under high pressure. They are less expensive and easier to maintain than pumps-driven models. They are however limited in their ability to create the ideal conditions for brewing since they only operate with 1-1.5 bar of pressure. The ideal 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 force hot water through the grounds and are significantly more portable than steam-driven electric machines.