How Does Machine Espresso Work?
Machine espresso employs precise pressure and mind-blowing filter technology to make the delicious coffee we enjoy. What exactly is it?
In order to make espresso, hot water is forced under high pressure through finely ground coffee. The process is similar to making drip coffee, but the difference is in the pressure.
The Group Head
The name implies the group head is the place you place your portafilter when brewing espresso. It is responsible for dispersing water into the portafilter, and controlling the pressure of the resulting extraction. There are many different types of group heads each with distinct advantages and drawbacks. Some are specifically designed for stability of temperature while others are specifically designed to handle pre-infusion. Some are designed to control the lever. Some include a combination such as the E61. This is a popular choice among baristas because it offers multiple benefits in a single package.
As you can see in the image above, the group head has numerous notches that you can put your portafilter, then twist it manually to secure it. There is also a gasket of rubber which is located inside the notches and helps create the seal when you insert your portafilter into the machine. The notches allow for the precise placement of the portafilter. This is crucial for an efficient extraction.
The group head is not just able to allow you to insert your portafilter easily however it also keeps a constant temperature. This is done by cycling hot water around the portafilter, and through the brew basin, ensuring the temperature is always right for extraction. It is important to note that even a small variation can mean the difference between a good and a great espresso.
The Pump
Motorized pumps in espresso machines rotary provide nine atmospheric bar pressure that is required for espresso extraction. This differs from manual piston machines which use levers. This pressure builds up by drawing 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 generally less expensive than piston-driven models, and they tend to last longer, however both types of machines may become damaged due to excessive use and poor cleaning. Pumps are also more complicated mechanically, which can raise prices of even simplest models.
Certain espresso machines utilize steam pressure instead of a pump in order to brew espresso. This can cause over-extraction because the boiler that makes steam also warms the water to boil. In addition these machines are often required to restore their pressure between cups, which requires time and energy.
A majority of espresso machines use an rotary or vibrating pump, with a vibration model using a rotating disc to create pressure, and rotating models that push hot water through the grounds at high speed. Both machines can produce excellent espresso, however rotary machines are more stable, quieter and less likely to break.
The Boiler
The boiler is the component which heats the water to the optimal temperature for extraction. The steam that is produced is then directed to the portafilter, which holds the espresso grounds. It is then pumped into the cup. During this process, steam creates pressure to push through the coffee grounds. This creates a layer crema on top. This is the hallmark of a great espresso.
There are three distinct types of espresso machines, each having distinct pumps and brew temperature. There are espresso machine uk to control the brew as well as the size of cup that can be made by the machine.
The earliest espresso machines were steam-based. They employed one boiler to create both steam and brew, however the pressure they were able to produce was not very high - two bars of atmospheric pressure, at most. This resulted in the coffee tasting burnt and bitter. The modern espresso machine was designed by the Milanese manufacturers Luigi Bezzerra & Desiderio Pavoni.
The most popular espresso machine is a semiautomatic model with an electric pump. When people think of espresso machines, they think of these machines. With a semi-automatic espresso machine, you need to grind the beans and tamp them by hand. The pump regulates the flow of water and pressure. This is a great compromise between the human touch and the mechanized quality.
The Filter
Espresso machines usually have filters that separate the grounds of the coffee from the hot water. The filter is also a vital component of the machine's temp control, since it helps to prevent overheating.
Filters also aid in flavor since it allows for a longer flowering period. This lets the beans release their nuances, and allows for better extraction.
However it is crucial to remember that even a top filter can result in a poor cup of coffee, because the quality of the beans and extraction is still essential.
This is where the magic happens. It's what makes espresso taste good. The grouphead, sometimes referred to as the brew head, is the place where the portafilter (the container you place the ground coffee in) is placed when making espresso.
Steam-driven espresso machines use hot water heated in an airtight container to create steam. The steam then pushes hot water through the grounds of coffee at high pressure. These types of machines tend to be less expensive and simpler to maintain than pump-driven models. They are however limited in their ability to create the perfect conditions for brewing, as they operate with 1-1.5 bar of pressure. The perfect shot requires 9-10 bars.
In recent times, espresso machines powered by compressed air-pump have become increasingly popular. They use an air compressor to force hot water through the grounds and are significantly more portable than electric steam-driven machines.