How Does Machine Espresso Work?
Machine espresso makes use of precise pressure and incredible filter technology to produce the perfect cup of coffee. How does it work exactly?
Espresso is produced by pushing hot water 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
As the name implies, the group head is where you place your portafilter while making espresso. It disperses the water into the portafilter, and regulates the pressure of extraction. There are several different types of group heads, each with their own advantages and disadvantages. Some focus on temperature stability, whereas others on pre-infusion options, and others are designed to control the lever. Some include a combination such as the E61. This is a preferred choice for baristas due to the fact that it has multiple advantages in a single package.
As you can see from the above photo, the group head has a number of notches. It is possible to place your portafilter in these notches, then twist the head to lock it. A gasket made of rubber is positioned in the notches to make a seal when you insert your portafilter. The notches on the head allow for a precise positioning of the portafilter which is vital for an efficient extraction.
The group head not only lets you to insert your portafilter easily, but it also maintains an even temperature. It does this by circulating hot water through the brew container and around the portafilter, making sure that it's always at the right temperature for extraction. This is vital, because just a few degrees could be the difference between a good and great espresso.
The Pump
In contrast to piston machines that are manually operated, which use a lever to pressurize water, the rotary espresso capsule machine machines use motorized pumps to supply the nine atmospheric bars of pressure necessary to extract espresso. The pressure is created by pumping water through a heat exchanger and then through the ground coffee.
Pumps are typically less expensive than piston-driven models, and they tend to last longer. However, both types of machines could degrade with overuse and insufficient cleaning. They also increase the complexity of mechanical systems which can result in the cost of even the simplest models.
Some espresso machines make use of steam pressure instead of a pump for brewing espresso. The drawback of this is that the same boiler that produces steam also raises the temperature of the water to the point of boiling which can cause over-extraction. In addition the machines often have to restore their pressure between cups, which requires time and energy.
Many retro espresso machine machines utilize either a rotary or vibration pump, which is 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, but rotary machines are quieter, more durable and less likely to fail.
The Boiler
The boiler is the component that heats water to an optimal temperature for extraction. The resulting steam reaches the portafilter, which contains the ground espresso coffee and is then pumped into the cup. During this process the steam causes enough pressure to push the grounds of coffee through. This results in a crema on the top of the espresso. This is a sign of a great espresso.
There are three types of espresso makers, and they differ in the type of pump they use and how hot the brew is. There are different ways to control the amount of brew, as well as the size of cup that can be produced by the machine.
The earliest espresso machines were steam type. They used one boiler to create steam and brew, but the pressure they could generate was low - only two bars of atmospheric pressure at the most. The coffee tasted bitter and burned. The modern espresso machine was invented by the Milanese producers Luigi Bezzerra & Desiderio Pavoni.
The most well-known espresso machine is a semiautomatic with an electric pump. This is what people envision when they think of an espresso machine. Semi-automatic machines require you to grind and tamp the beans on your own, but the pump regulates the water flow and pressure. This is a great compromise between the human touch and mechanized quality.
The Filter
compact espresso machine machines typically have a filter that separates the grounds of the coffee from hot water. The filter is also a vital part of the temperature control system because it stops the machine from overheating.
A filter also improves flavor as it allows for a longer flowering phase. This allows the beans bean to cup espresso machine let their nuances out, and improves extraction.
It is important to remember that even the best filter can result in a bad cup of coffee. The quality of the beans, and the extraction process, are still crucial.
It's in this area that the magic happens. This is what makes espresso taste so good. The grouphead (also known as the brewhead) is where you place the portafilter, the device which you put the coffee grounds in, when making espresso machine coffee.
Steam-driven espresso machines use hot water that is heated inside an airtight vessel to create steam. The steam then moves hot water through the coffee grounds under high pressure. These types of machines tend to be less expensive and easier to maintain than pumps-driven models. However, they are limited in their capacity to create the ideal brewing conditions, since they operate at 1-1.5 bars of pressure. The perfect shot requires 9-10 bar.
In recent years, espresso machines powered by a compressed air pump have become increasingly popular. They utilize an air compressor to force hot water through the grounds and are much more portable than electric steam-driven machines.