How Does Machine Espresso Work?
Machine espresso uses precision 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 forced under high pressure through finely ground coffee. The process is similar to making drip coffee. However the pressure is the major difference.
The Group Head
The name implies the group head is where you put your portafilter in when brewing espresso. It is responsible for dispersing the water into the portafilter and controlling the pressure that results from the extraction. There are many different kinds of group head, each with their own advantages and drawbacks. Some focus on temperature stability, others on pre-infusion capabilities, and still others are designed to control the lever. There are some that have a combination of features, such as the E61, which is considered the classic choice among many baristas due to its ability to provide multiple benefits in one package.
As you can see in the photo above the group head is made up of several notches to place your portafilter and twist it by hand to lock it in. There is also a gasket made of rubber which is located inside the notches, which helps create an airtight seal after inserting your portafilter into the machine. The notches on the head permit an exact positioning of the portafilter which is essential to ensure an efficient extraction.
The group head not only lets the portafilter to be inserted easily however, it also keeps a constant temperature. This is achieved by cycling hot water around the portafilter and through the brew-basket, making sure the temperature is always right to extract the coffee. This is vital, because even a few degrees can make the difference between good and excellent espresso.
The Pump
The motorized pumps that are used in rotary espresso machines provide the nine atmospheric bar pressure required to extract espresso. This differs 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 shot through the ground coffee inside the group head.
Pumps are typically less expensive and last for longer than piston-driven machines. However, both types of machines may degrade because of excessive use and poor cleaning. They also make mechanically complex, which can result in the cost of even the simplest models.
Certain espresso machines utilize steam pressure instead of a pump for brewing espresso. This can result in over-extraction because the boiler that makes steam also heats the water to boil. In addition, these machines frequently have to restore their pressure between cups, which requires time and energy.
Many espresso machines use a rotary or vibration pump. A vibration model makes use of a rotating disk to generate pressure, while a rotating model pushes hot water through the ground at a high speed. Both machines produce great espresso, but rotary machines are more stable, quieter and less likely to break.
The Boiler
The boiler is the one that makes the water warm to the right temperature for extraction. The steam that is produced reaches the portafilter containing the ground espresso and is then funneled down into the cup. The steam creates pressure and pushes through the coffee grounds. This results in a layer crema that is then poured over. This is one of the hallmarks of a good espresso.
There are three kinds of espresso makers, and they differ in the type of pump they employ and the degree of heat that the brew is. There are a variety of ways in which the brew could be controlled as well as the size of the cup that the maker can create.
The first espresso machines were steam-types. They employed one boiler to make both steam and brew however the pressure they were able to create was minimal - two bars of atmospheric pressure at most. This resulted in the coffee tasting bitter and burnt. This is the reason why Milanese manufacturers Luigi Bezzerra and Desiderio Pavoni invented the modern espresso machine.
The most common espresso maker is a semi-automatic device with an electric pump. These are the images people have when they imagine an espresso machine. With a semi-automatic machine you must grind the beans and then tamp them by hand. However, small espresso machine is able to regulate the flow of water and pressure. This is an excellent solution that combines human control with mechanised accuracy.
The Filter
Typically, espresso machines employ filters to separate the coffee grounds as they pass through the hot water. The filter is also an essential element of the machine's temperature control, since it stops overheating.
It also improves flavor, since a filter allows for a more prolonged bloom time. This lets the beans release their flavors, and allows for better extraction.
It is important to keep in mind that even the best filter can result in a bad cup of coffee. The quality of the beans, as well as the extraction, remain vital.
This is where the magic happens, it's what makes an espresso really taste good. The grouphead (also known as the brewhead) is where you put the portafilter, the device used to place the grounds of your coffee into when making espresso.
Steam-driven espresso machines use hot water that is heated inside an airtight vessel to create steam. The steam then pushes hot water into the grounds of coffee at high pressure. These kinds of machines are usually less expensive and simpler to maintain than pump-driven models. However, they are limited in their ability to provide 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, compressed-air-pump-driven espresso machines have become more popular. They use an air-compressor to push hot water across the ground. They are also more mobile than steam-driven electric espresso machines.