How Does Machine Espresso Work?
Machine espresso makes use of precise pressure and mind-blowing filter technology to create the perfect cup of coffee. But how exactly does it work?
Espresso is created by forcing hot water under pressure through finely ground coffee. The process is similar to that of making drip coffee. However the pressure is the primary difference.
The Head of the Group
As the name suggests, the group head is the place you place your portafilter while brewing espresso. It disperses water into the portafilter, and then controls the pressure of the extraction. There are many different types of group heads each with its own advantages and drawbacks. Some are focused on temperature stability, while others on pre-infusion features, and others are designed to control the lever. Some include a combination like the E61. This is a preferred choice for baristas as it provides a variety of benefits in one package.
As you can see in the above photo the group head is made up of 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 that resides inside the notches, which helps create the seal when you insert your portafilter into the machine. The notches on the head allow for a precise location of the portafilter which is crucial to ensure an efficient extraction.
Apart from allowing you easily insert your portafilter, the group head is responsible for maintaining an even temperature. This is achieved by cycling hot water around the portafilter, and through the brew basin, ensuring that the temperature is at the right level for extraction. It is important to realize that even a small differences can make the distinction between a good and a excellent espresso.
The Pump
In contrast to manual piston machines which rely on a lever that pressurize water, rotating espresso machines rely upon motorized pumps to supply the nine atmospheric bars of pressure required for espresso extraction. The pressure is created by pumping water through a heat exchanger and then through the ground coffee.
Pumps tend to be more affordable and last longer than piston-driven machines. However, both kinds of machines can degrade because of excessive use and insufficient cleaning. Pumps are also more complex mechanically, which can increase the cost of even the simpler models.
Some espresso machines do away with the pump entirely and use steam pressure to brew espresso. This can cause over-extraction because the boiler that makes steam also causes the water to boil. The machines must also constantly rebuild their pressure in between cups. This requires energy and time.
Many espresso machines utilize a vibration or rotary pump, which has a vibration model using a rotating disc that generates the pressure and rotating models that push hot water through the grounds at high speed. Both types of machine can produce an excellent espresso, but the rotary models are quieter and more durable than vibration pumps.
The Boiler
The boiler is the part which heats the water to the optimal temperature to extract. The resultant steam then reaches the portafilter containing the ground espresso coffee and is then funneled down into the cup. The steam causes enough pressure to push the grounds of the coffee through. This results in a layer of crema that is then poured over. This is a hallmark of a great espresso.
There are three kinds of espresso makers, and they differ in the type of pump they use and how hot the brew is. There are various ways to control the amount of brew, as well as the size of cup that can be produced by the machine.
The first espresso machines were steam-based. They utilized one boiler to create both steam and brew, however, the pressure they could produce was very low - just two bars of atmospheric pressure at the most. The coffee tasted bitter and burnt. This is why the Milanese makers Luigi Bezzerra and Desiderio Pavoni invented the modern espresso machine.
The most commonly used espresso machine is a semiautomatic that has an electric pump. These are the things people think of when they think of an espresso machine. Semi-automatic machines require you to grind and tamp the beans yourself while the pump controls the water flow and pressure. This is a great compromise between the human touch and the mechanised quality.
The Filter
Typically, espresso machines have filters that separate the grounds of coffee as they move through the hot water. The filter is also a crucial element of the temperature control system, since it helps prevent the machine from overheating.
A filter also helps with flavor as it allows for the beans to flower for a longer period of time. previous helps the beans to release their nuances and gives an opportunity to improve extraction.
However it is crucial to remember that even a great filter can result in a poor cup of coffee, as the quality of the beans and extraction is important.
It's in this area that the magic happens. This is what makes espresso taste so delicious. The grouphead (also called the brewhead) is where you place the portafilter, the thingy that you put the coffee grounds in, when making espresso.
Steam-driven espresso machines use hot water that is heated inside an airtight container to make steam. The steam then pushes hot water through the grounds of coffee at high pressure. These machines are cheaper and are easier for the user to maintain than pumps-driven models. They are however limited to create the perfect conditions for brewing since they only operate with 1-1.5 bar of pressure. The perfect shot requires 9-10 bars.
In recent years, compressed air-driven espresso machines have been gaining popularity. They utilize an air compressor to force the hot water through the grounds, and are far more portable than steam-driven electric machines.