How Does Machine Espresso Work?
The machine espresso makes use of precise pressure and filtering system that is awe-inspiring to make the coffee you enjoy. How does it work exactly?
In order to make espresso, hot water is pushed under pressure through finely ground coffee. The process is similar to that of making drip coffee. However it is the pressure that makes the main difference.
The Group Head
The group head is the portafilter you insert when brewing espresso. machines espresso machines disperses the water into the portafilter, and regulates the pressure of the extraction. There are many different types of group heads, each with its own advantages and disadvantages. Some are designed to provide stability in temperature, while others are specifically designed to handle pre-infusion. Some are designed to control the lever. Some have a combination, such as the E61. This is a popular choice among baristas as it provides a variety of advantages in a single package.
As you can see in the image above the group head is made up of numerous notches that you can put your portafilter, then twist it manually to secure it. A gasket made of rubber is placed in the notches to create a seal when you insert your portafilter. The notches on the head permit an exact position of the portafilter which is necessary for an efficient extraction.
Apart from allowing you easily place your portafilter in, the group head is also responsible for maintaining a consistent temperature. This is done by cycling hot water around the portafilter and through the brew basin, ensuring that the temperature is always at the right level to extract the coffee. This is important, as even a small difference in temperature can be the difference between a excellent and great espresso.
The Pump
Contrary to manual piston machines which rely on a lever that pressurize water, rotary espresso machines rely on motorized pumps to supply the nine atmospheric bars of pressure required for espresso extraction. This pressure is built up by pumping water through a heat exchanger and then through the ground coffee.
Pumps are generally less expensive than piston-driven machines, and they tend to last longer, however both types of machines may get damaged through overuse and lack of cleaning. Pumps are also more complicated mechanically, which can raise prices of even simpler models.
Some espresso machines use steam pressure instead of a pump to brew espresso. The disadvantage of this is that the boiler that produces steam also increases the temperature of the water to boiling and can result in excessive extraction. Additionally the machines often have to rebuild their pressure between cups, which requires time and energy.
Many espresso machines make use of an rotary or vibrating pump, which has a vibration model using a rotating disc to create pressure, and an rotary model that pushes hot water through the grounds at high speed. Both machines can make great espresso, however rotary machines are more stable, quieter and less likely to break down.
The Boiler
The boiler is the part that heats water to the ideal temperature to extract. The resulting steam reaches the portafilter which holds the ground espresso and is then pumped into the cup. The steam generates enough pressure to push the coffee grounds through. This results in a whipped-up top of the espresso. This is one of the main characteristics of a great espresso.
There are three kinds of espresso makers. They differ in the type of pump they use and the degree of heat that the brew is. There are various ways to control the amount of brew, as well as the size of cup that can be produced by the machine.
The first espresso machines were steam-type. They used one boiler to make both 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. This is why Milanese producers Luigi Bezzerra and Desiderio Pavoni invented the modern espresso machine.
The most common espresso maker is a semi-automatic machine that has an electric pump. When people think of espresso machines, they envision these machines. Semi-automatic machines require you to grind and tamp your beans yourself while the pump controls the flow of water and pressure. This is a great compromise between human control and mechanized consistency.
The Filter
Typically, espresso machines employ a filter to separate out the grounds of coffee as they move through the hot water. The filter is also an essential component of the machine's temp control, since it helps to prevent overheating.
A filter can also help with flavor as it allows for a longer flowering phase. This allows the beans to release their flavors, and also allows for better extraction.
It is important to keep in mind that even the finest filter could result in a poor cup of coffee. The quality of the beans, and the extraction, are still very important.
It's in this area that the magic happens. This is what makes espresso taste so delicious. The grouphead (also known as the brewhead) is where you put the portafilter - the thingy used to place the coffee grounds in, while making espresso.
Steam-driven espresso machines use hot water that is heated in an airtight vessel to create steam. The steam then pushes hot water through grounds of the coffee under pressure. These types of machines are typically less expensive and easier to maintain than pumps-driven models. However, they are limited in their ability to create the perfect brewing conditions since they operate at 1-1.5 bars of pressure. The perfect shot requires 9-10 bar.
In recent years, compressed air pump-driven espresso machines have become more popular. They make use of an air compressor to force hot water through the ground. They are also more mobile than steam-driven electric espresso machines.