How Does Machine Espresso Work?
Machine espresso uses precision pressure and incredible filter technology to produce the delicious coffee we enjoy. How does it work exactly?
Espresso is made 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 insert when brewing espresso. It is responsible for dispersing water into the portafilter and then controlling the pressure of the resulting extraction. There are various kinds of group heads, each with their particular advantages and disadvantages. Some are designed to provide temperature stability while others are designed to handle pre-infusion. Some are designed to control the lever. Some include a mix of features, like the E61 one, which is the most popular choice among baristas because of its ability to provide multiple benefits in one package.
As you can see from the above photo, the group head is equipped with several notches. You place your portafilter inside these notches, and then twist the head to lock it. There is also a gasket made from rubber that is a part of the notches, which helps create a seal when you insert your portafilter into the machine. The notches allow for precise placement of the portafilter. This is vital for a consistent extraction.
In addition to allowing you to easily insert your portafilter, the group head is also responsible for maintaining a consistent temperature. It does this by circulating hot water through the brew pan and around the portafilter to ensure that it's always at the correct temperature to extract. This is crucial, since even a few degrees can make the difference between excellent and great espresso.
The Pump
The motorized pumps that are used in rotary espresso machines supply the nine atmospheric bars of pressure required to extract espresso. This differs from manual piston machines which use a lever. The pressure builds by removing 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 generally less expensive than piston-driven models, and they tend to last longer. However, both types of machine can become damaged due to excessive use and poor cleaning. They also add mechanical complexity that can lead to the cost of even the simplest models.
Certain espresso machines utilize steam pressure instead of a pump to make espresso. The drawback of this is that the same boiler that produces steam also increases the temperature of water until it reaches boiling and can result in excessive extraction. In addition these machines typically have to restore their pressure between cups, which requires time and energy.
Many espresso machines make use of the rotary or vibration pump, which is a vibration model that uses a vibrating disc to generate the pressure and rotating models that push hot water through the grounds under high speed. Both models can produce an excellent espresso, however the rotary models are quieter and more durable than vibration pumps.
The Boiler
The boiler is the element which heats the water to the optimal temperature for extraction. The resulting steam is then transferred to the portafilter, which contains ground espresso beans and is then funneled down into the cup. During this process the steam generates enough pressure to push the grounds of the coffee through. This creates a foam on the top of the espresso. This is a hallmark of a great espresso.
There are three types of espresso machines, each with different pumps and the temperature of the brew. There are different ways that the brew can be controlled as well as the size of the cup that the machine can produce.
The first espresso machines were steam-type. They had one boiler to create steam and brew, however, the pressure they could generate was low - only two bars of atmospheric pressure maximum. This resulted in the coffee tasting burnt and bitter. This is the reason why Milanese makers Luigi Bezzerra and Desiderio Pavoni developed the modern espresso machine.
The most well-known espresso maker is a semiautomatic machine with an electric pump. These are what people imagine when they imagine an espresso machine. With a semi-automatic espresso machine, you need to grind the beans and tamp them yourself but the pump controls the flow of water and pressure. This is a fantastic compromise between human control and mechanized reliability.
The Filter
Typically, espresso machines have a filter to separate out the grounds of coffee when they pass through the hot water. best cheap espresso machine is also a vital element of the temperature control system as it keeps the machine from overheating.
It also improves flavor, as a filter allows for a more prolonged bloom time. This allows the beans to release their flavor and gives an opportunity to improve extraction.
It is important to keep in mind that even the best filter can make a bad cup of coffee. The quality of the beans as well as the extraction, are still very important.
This is where the magic happens. It's what makes an espresso really taste great. The grouphead, also called the brew head, is where the portafilter (the device you put the ground coffee into) sits when you're making espresso.
Steam-driven espresso machines use hot water that is heated inside an airtight container to create steam. The steam then moves hot water through the grounds of coffee under high pressure. These kinds of machines are generally less expensive and easier to maintain than pumps-driven models. They are however limited to create the ideal conditions for brewing since they only operate with 1-1.5 bar of pressure. The perfect shot requires 9-10 bars.
In recent years, espresso machines powered by a compressed air pump have become increasingly popular. They use an air-compressor to force hot water into the ground, and are more mobile than electric steam-driven espresso machines.