How Does Machine Espresso Work?
Machine espresso utilizes precise pressure and mind-blowing filter technology to create the coffee we love. But how exactly does it work?
In order to make espresso hot water is pushed under pressure through finely ground coffee. The process is similar to making drip coffee but the key difference is in the pressure.
The Group Head
The group head is the portafilter that you insert when brewing espresso. It disperses the water into the portafilter, and regulates the pressure during the extraction. There are many different types of group heads each with distinct advantages and disadvantages. Some are specifically designed for the stability of temperature while some are built to handle pre-infusion. Others are built to control the lever. There are some that have a combination of features, such as the E61 that is the standard choice for many baristas due to its capacity to offer multiple perks in a single package.
As you can see from the above photo the group head is fitted with several notches. You can place your portafilter inside these notches, and then turn the head around to secure it. A rubber gasket is located in the notches to create a seal while you insert your portafilter. The notches on the head permit an exact position of the portafilter which is crucial for a consistent extraction.
The group head not only allows you to place your portafilter easily, but it also maintains the temperature at a constant level. This is done by cycling hot water around the portafilter, and through the brew-basket to ensure that the temperature is constant for extraction. It is important to note that even a tiny difference can make the difference between a good and great espresso.
The Pump
In contrast to piston machines that are manually operated, which rely on a lever to pressurize water, rotary espresso machines rely on motorized pumps to supply the nine atmospheric bars of pressure necessary for espresso extraction. The pressure builds by removing tap water from a reservoir and pumping it through a heat exchanger before being shot through the ground coffee inside the group head.
Pumps are typically less expensive than piston-driven models, and they tend to last longer, however both types of machines may be damaged by excessive use and inadequate cleaning. Pumps are also more complicated mechanically, which could increase prices of even simpler models.
Certain espresso machines remove the pump completely and use steam pressure to brew espresso. The disadvantage of this is that the same boiler that produces steam also increases the temperature of water to boiling which can cause excessive extraction. The machines must also constantly rebuild their pressure between cups. This takes energy and time.
A majority of espresso machines use the rotary or vibration pump, which has a vibration model using a vibrating disc that generates the pressure and the rotary model pushing hot water through the grounds at high speed. Both types of machines can make excellent espresso, however the rotary models are quieter and more durable than vibration pumps.
The Boiler
The boiler is the part that heats water to the ideal temperature for extraction. The steam that is created reaches the portafilter, which contains the espresso coffee grounds. The steam best espresso machine is then channeled into the cup. The steam creates enough pressure to push the coffee grounds through. This creates a crema on top of the espresso. This is the hallmark of a great espresso.
There are three types of espresso machines, each having different pumps and the temperature of the brew. There are different ways to control the brew and the size of cup that can be produced by the machine.
The first espresso machines were steam types. They had one boiler to make steam and brew, however the pressure they were able to create was minimal - two bars of atmospheric pressure maximum. The coffee tasted bitter and burnt. This is the reason why Milanese producers Luigi Bezzerra and Desiderio Pavoni created the modern espresso machine.
The most common espresso machine is a semiautomatic one with 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 on your own however the pump controls the flow of water and pressure. This is an excellent combination of human control and mechanized accuracy.
The Filter
Espresso machines usually have a filter that separates the grounds of coffee from hot water. The filter is also an important element of the temperature control system, since it helps prevent the machine from overheating.
A filter also improves flavor, as it permits a longer flowering phase. This allows the beans to release their flavors, and allows for a better 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 and the extraction, remain vital.
It's here that the magic takes place. This is the reason why espresso tastes so delicious. The grouphead (also called the brewhead) is where you put the portafilter, which is the thingy which you put the grounds of coffee into while making espresso.
Steam-driven espresso machines make use of hot water that is heated in an airtight container to make steam. The steam then pushes hot water through the coffee grounds under high pressure. These kinds of machines are usually less expensive and simpler to maintain than pumps-driven models. They are however limited in their ability for creating 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, compressed air-driven espresso machines have been gaining popularity. They make use of an air compressor to push hot water across the ground. They are also more mobile than steam-driven electric espresso machines.