How Does Machine Espresso Work?
Machine espresso utilizes precise pressure and incredible filter technology to produce the coffee we love. How does it work exactly?
Espresso is produced by pushing hot water under high pressure through finely-ground coffee. The process is similar to making drip coffee however the main difference lies in the pressure.
The Group Head
The group head is the portafilter you put in when making espresso. It is responsible for dispersing water into the portafilter, and controlling the pressure of the resulting extraction. There are many different types of group heads each with its own advantages and disadvantages. Some focus on temperature stability, while others on pre-infusion capabilities, and still others are designed to control the lever. Some have a combination of features, such as the E61, which is to be the most popular among baristas for its ability to provide multiple benefits in one package.
As you can see in the photo above The group head features numerous notches that you can put your portafilter, then twist it by hand to secure it. There is also a gasket made of rubber that is a part of the notches, which helps create the seal when you insert your portafilter into the machine. The notches permit precise placement of your portafilter. This is vital for an efficient extraction.
Apart from allowing you easily connect your portafilter, the group head is also responsible for maintaining an even temperature. It does this by circulating hot water through the brew basket and around the portafilter, making sure that it's always at the correct temperature for extraction. It is important to note that even a tiny differences can make the distinction between a good and excellent espresso.
The Pump
The motorized pumps used in rotary espresso machines provide the nine atmospheric bar pressure required for espresso extraction. This differs from manual piston machines that rely on levers. The pressure is created by pumping water through a heat-exchanger and then through the ground coffee.
Pumps tend to be cheaper than piston-driven models, and they tend to last longer, however both types of machines may get damaged through overuse and lack of cleaning. They also increase the complexity of mechanical systems and can lead to a high price tag on even the simplest models.
Certain espresso machines can eliminate the pump completely and instead utilize steam pressure to make espresso. The downside is that the same boiler that produces steam also raises the temperature of water to the point of boiling, which can lead to excessive extraction. The machines must also continuously rebuild their pressure between cups. This requires energy and time.
Many espresso machines use an rotary or a vibration pump. A vibration model uses a rotating disk to generate pressure, whereas a rotating model pushes hot water through the ground at high speed. Both types of machine can make a great espresso, however the rotary models are quieter and more durable than vibration pumps.
The Boiler
The boiler is the element that heats the water to the optimal temperature to extract. The steam that is created is then directed to the portafilter, which holds the espresso grounds. It is then poured into the cup. During this process, steam creates pressure and pushes through the grounds of the coffee. This creates a foam on the top of the espresso. This is one of the hallmarks of a good espresso.
There are three types of espresso makers. They differ in the kind of pump they use and the degree of heat that the coffee is. There are a variety of ways that the brew can be controlled as well as the size of the cup the machine can make.
The first espresso machines were steam type. They employed a single boiler to make both steam and brew but the pressure they could generate was low - only two bars of atmospheric pressure at most. The coffee tasted bitter and burnt. The modern espresso machine was invented by the Milanese producers Luigi Bezzerra & Desiderio Pavoni.
The most well-known espresso machine is a semiautomatic with an electric pump. When people think of espresso machines, they picture these machines. Semi-automatic machines require you to grind and tamp the beans by yourself however the pump controls the water flow and pressure. This is a perfect compromise between human control and mechanized consistency.
The Filter
Typically, espresso machines use filters that separate the grounds of coffee as they move through the hot water. The filter is also an important element of the temperature control system as it prevents the machine from overheating.
It also enhances flavor, since a filter allows for a longer bloom phase. This lets the beans release their flavor and allows for better extraction.
It is important to keep in mind that even the best filter could result in a poor cup of coffee. The quality of the beans and the extraction process, 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 place the portafilter, the device used to place the grounds of your coffee into when making espresso.
In an espresso machine that is driven by steam, hot water is heated in an airtight container to create steam. This is then pushed through the grounds at a high pressure. They are less expensive and easier for the owner to maintain than pumps-driven models. However, they are limited in their capacity to create the ideal brewing conditions, since they operate at 1-1.5 bars of pressure, while the perfect shot requires 9-10 bar.
In coffee and espresso machine , espresso machines powered by a compressed air pump have become increasingly popular. They use an air-compressor to force hot water through the ground and are much more mobile than steam-driven electric espresso machines.