How Does Machine Espresso Work?

The machine espresso uses precise pressure, as well as a filtering system that is awe-inspiring to make the coffee you enjoy. What exactly is it that makes it work?

Espresso is created by forcing hot water under high pressure through finely ground coffee. The process is similar to making drip coffee but the key difference is in the pressure.

The Head of the Group

The group head is the portafilter you put in when making espresso. It disperses the water into the portafilter, and controls the pressure of the extraction. There are several different types of group heads, each with their own advantages and drawbacks. Some are focused on temperature stability, some on pre-infusion options, and others are designed to control the lever. Some include a combination such as the E61. This is a favorite among baristas because it offers multiple advantages in one package.

As you can see from the image above, the group head has a number of notches. You can place your portafilter into these notches and twist the head to secure it. There is also a gasket made from rubber that is a part of the notches and helps to create the seal when you insert your portafilter into the machine. The notches allow for precise placement of the portafilter. This is vital for an accurate extraction.

The group head does not just allow the portafilter to be inserted easily however, it also keeps a constant temperature. This is accomplished by cycling hot water around the portafilter and through the brew-basket to ensure that the temperature is constant for extraction. This is important, as just a few degrees could mean the difference between good and great espresso.

The Pump

Contrary to manual piston machines which rely on a lever that pressurize water, the rotary espresso machines use motorized pumps that provide the nine atmospheric bars of pressure needed for espresso extraction. The pressure is built by pumping water through a heat exchanger and then through the ground coffee.

Pumps tend to be cheaper than piston-driven machines and tend to last longer. However, both types of machines can degrade with overuse and insufficient cleaning. Pumps are also more complex mechanically, which can raise the price of even the simplest models.

Certain espresso machines can eliminate the pump entirely and use steam pressure to brew espresso. This could lead to over-extraction since the boiler that produces steam also warms the water to boil. These machines also have to continually rebuild their pressure between cups. This takes energy and time.

Many espresso machines make use of a vibration or rotary pump, with a vibrating model using a rotating disc to create the pressure, and an rotary model that pushes hot water through the grounds at high speed. Both machines can produce excellent espresso however rotary machines tend to be more quiet, durable and less likely to fail.

The Boiler

The boiler is used to heat the water to the right temperature to extract. The steam that is created reaches the portafilter, which is a container for espresso grounds. It is then poured into the cup. The steam creates pressure that pushes through the coffee grounds. This results in a layer of crema on top. This is one of the hallmarks of a great espresso.

There are three different types of espresso machines, each having different types of pumps and the temperature of the brew. There are different ways to control the strength of the brew and the size of the cup that can be made by the machine.

The first espresso machines were steam-types. They utilized one boiler to create steam and brew, however, the pressure they could create was minimal - two bars of atmospheric pressure maximum. The coffee tasted bitter and burnt. The modern espresso machine was developed by the Milanese makers Luigi Bezzerra & Desiderio Pavoni.

The most popular espresso maker is a semiautomatic machine with an electric pump. This is what people envision when they imagine an espresso machine. With a semi-automatic espresso machine, you have to grind the beans and then tamp them by hand, but the pump controls the flow of water and pressure. This is a fantastic combination of human control and mechanized consistency.

The Filter

professional espresso machine machines usually use a filter that separates the coffee grounds from the hot water. The filter is also a vital component of the machine's temp control, as it prevents overheating.

Filters also aid in flavor, as it permits an extended flowering time. This allows the beans to let their nuances out and provides an opportunity for better extraction.

It is important to keep in mind that even the best filter could result in a poor 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 the thing that makes espresso taste good. The grouphead, sometimes called the brew head, is where the portafilter (the device you put the coffee grounds into) is placed when you're making espresso.

In a steam-driven espresso machine hot water is heated in an airtight container to create steam, which is then pushed through the grounds with high pressure. These machines are cheaper and are easier for the user to maintain than pumps-driven models. They are however limited for creating the ideal conditions for brewing, as they operate with 1-1.5 bar of pressure. The ideal shot requires 9-10 bars.

In recent years, compressed air pump-driven espresso machines have become more popular. They use an air compressor to push the hot water through the grounds, and are far more portable than steam-driven electric machines.