How Does Machine Espresso Work?
The machine espresso uses precise pressure, as well as a filter technology that is mind-blowing to create the coffee you enjoy. What exactly is it that makes it work?
To make an 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 group head is the portafilter that is inserted when you are making espresso. It is responsible for dispersing the water into the portafilter, and controlling the pressure that results from the 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 features, and others are designed to control the lever. Some come with a combination of both, like the E61. This is a favorite among baristas since it provides multiple advantages in one package.
As you can see from the image above the head of the group is fitted with several notches. You can place your portafilter in these notches and then turn the head around to secure it. There is also a gasket of rubber in the notches and helps create the seal when you insert your portafilter into the machine. The notches allow for an exact placement of the portafilter. This is crucial for an even extraction.
The group head not only lets you to put in your portafilter easily but also maintains the same temperature. This is done by cycling hot water around the portafilter and through the brew-basket, making sure that the temperature is always at the right level to extract the coffee. This is important, as even a small difference in temperature can make the difference between a good and great espresso.
The Pump
The motorized pumps that are used in rotary espresso machines provide the nine atmospheric bar pressure needed for espresso extraction. This differs from manual piston machines that use a lever. The pressure builds up by drawing tap water from a reservoir and pumping it through a heat exchanger before it is shot through the ground coffee inside the group head.
Pumps are typically more affordable and last longer than piston-driven machines. However, both types of machines can deteriorate because of frequent use and insufficient cleaning. Pumps are also more complicated mechanically, which could increase the cost of even most basic models.
Some espresso machines employ steam pressure instead of a pump to make espresso. The disadvantage of this is that the same boiler that produces steam also raises the temperature of water to the point of boiling which could lead to over-extraction. Additionally the machines often have to restore their pressure between cups, which takes time and energy.
A large majority of espresso machines employ either a vibration or rotary pump. A vibration model makes use of a vibrating disk to generate pressure, while a Rotary model pushes hot coffee through the ground at a fast speed. Both types of machines can make excellent espresso, but Rotary machines are quieter and more durable than vibration pumps.
The Boiler
The boiler is the one that makes the water warm to a temperature that is ideal for extraction. The steam that is created is then directed to the portafilter, which holds the espresso grounds. It is then pumped into the cup. During this process the steam causes enough pressure to push the grounds of the coffee through. This creates a crema on the top of the espresso. This is one of the main characteristics of a good espresso.
There are three different types of espresso machines, each with distinct pumps and the temperature of the brew. There are various ways to control the amount of brew, as well as the size of the cup that can be produced by the machine.
The first espresso machines were steam-type. They employed one boiler to create both steam and brew however the pressure they were able to create was minimal - two bars of atmospheric pressure, at most. The coffee tasted bitter and burned. The modern espresso machine was invented by the Milanese makers Luigi Bezzerra & Desiderio Pavoni.
The most well-known espresso maker is a semi-automatic device with an electric pump. These are what people imagine when they imagine an espresso machine. Semi-automatic machines require you to grind and tamp the beans on your own while the pump controls the flow of water 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 the coffee as they go through the hot water. The filter is also an important part of the temperature control system as it prevents the machine from overheating.
It also improves flavor as a filter allows for a more prolonged bloom phase. This allows the beans to release their flavor and allows for a better extraction.
However, it is important to more info remember that even a good filter could result in a bad cup of coffee as the quality of the beans and extraction are important.
This is where the magic happens, it's the thing that makes an espresso really taste good. The grouphead, also referred to as the brewhead, is where the portafilter (the thing you put the coffee grounds into) sits when you're making espresso.
In the steam-driven espresso machine hot water is heated in an airtight container to create steam. This is then pushed through the grounds with high pressure. These types of machines are typically cheaper and easier to maintain than pump-driven models. However, they are limited in their capacity to create the ideal conditions for brewing as they only operate at 1-1.5 bars of pressure. While the perfect shot requires 9-10 bar.
In recent times, espresso machines powered by compressed air-pump have become increasingly popular. They utilize an air compressor to push hot water through the ground and are much more mobile than electric steam-driven espresso machines.