How Does Machine Espresso Work?
Machine espresso makes use of precise pressure and mind-blowing filter technology to make the perfect cup of coffee. What exactly is it that makes it work?
To make espresso, hot water is forced under high pressure through finely ground coffee. The process is similar to making drip coffee but the key difference is in the pressure.
The Group Head
As the name implies, the group head is where you put your portafilter in when brewing espresso. It is responsible for dispersing water into the portafilter and controlling the pressure that results from the extraction. There are several different types of group head, each with their particular advantages and drawbacks. Some are designed for the stability of temperature while some are specifically designed to handle pre-infusion. Others are made to control the lever. There are also some that include a mix of features, such as the E61, which is the standard choice for many baristas because of its ability to offer multiple perks in a single package.
As you can see from the photo above the group head has a number of notches. It is possible to place your portafilter in these notches, then turn the head around to secure it. A rubber gasket is located in the notches to make a seal when you insert your portafilter. The notches on the head permit an exact location of the portafilter which is essential for an efficient extraction.
The group head does not just allow you to place your portafilter easily but also maintains an even temperature. It does this by cycling hot water through the brew pan and around the portafilter, making sure that it is always at the right temperature for extraction. It is important to realize that even a tiny deviation can make the difference between a great and a excellent espresso.
The Pump
Contrary to manual piston machines which rely on a lever that pressurize water, the rotary espresso machines use motorized pumps to supply the nine atmospheric bars of pressure that are required to extract espresso. The pressure is built 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, but both types of machine can be damaged by excessive use and inadequate cleaning. Pumps are also more complex mechanically, which can increase the cost of even most basic models.
Certain espresso machines eliminate the pump entirely and utilize steam pressure to make espresso. This can result in over-extraction because the boiler that makes steam also warms the water to boil. They also have to constantly rebuild their pressure in between cups. This requires energy and time.
Many espresso machines make use of an rotary or a vibration pump. A vibration model employs a rotating disk to generate pressure, while the Rotary model pushes hot coffee through the ground at a rapid speed. Both machines can make great espresso, but rotary machines are more stable, quieter and less likely to break.
The Boiler
The boiler is the one that will heat the water to the ideal temperature to extract. The steam that is produced reaches the portafilter, which is the container that holds the espresso coffee grounds. It is then pumped into the cup. During this process the steam causes enough pressure to push the coffee grounds through. This creates a layer crema on top. This is one of the hallmarks of a good espresso.
There are three kinds of espresso makers, which differ in the kind of pump they use and how hot the coffee is. There are also different ways in which the brew can be controlled, as well as the dimensions of the cup 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 could generate was low - only two bars of atmospheric pressure, at most. This led to the coffee tasting burnt and bitter. The modern espresso machine was invented by the Milanese makers Luigi Bezzerra & Desiderio Pavoni.
The most well-known espresso maker is a semiautomatic machine with an electric pump. These are the images people have when they think of an espresso maker. With a semi-automatic espresso machine, you have to grind the beans and tamp them by hand, but the pump regulates the flow of water and pressure. This is a fantastic combination of human espresso coffee machine control and mechanized consistency.
The Filter
Typically, espresso machines have a filter to separate out the grounds of coffee as they move through the hot water. The filter is also an important part of the temperature control system, since it helps prevent the machine from overheating.
A filter also improves flavor, as it permits the beans to flower for a longer period of time. This lets the beans release their nuances, and allows for a better extraction.
However it is crucial to keep in mind that even a top filter could result in a bad cup of coffee, as the quality of the beans and extraction is essential.
It's in this area that the magic occurs. This is the reason why espresso tastes so good. The grouphead, also referred to as the brewhead, is where the portafilter (the container you place the ground coffee into) is placed when you're making espresso.
In a steam-driven espresso machine, hot water is heated in an airtight container to create steam. Steam then pushes the hot water through the grounds under high pressure. These kinds of machines are generally cheaper and easier to maintain than pumps-driven models. However, they are limited in their capacity to create the ideal brewing conditions, as they only operate at 1-1.5 bars of pressure. The perfect shot requires 9-10 bar.
In recent years, espresso machines powered by a compressed air pump have become increasingly popular. They use an air compressor to push hot water through grounds, and are far more portable than electric steam-driven machines.