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How Does Machine Espresso Work?

Machine espresso uses precision pressure and incredible filter technology to produce the perfect cup of coffee. How does it work exactly?

Espresso is created by forcing hot water at high pressure through finely ground coffee. The process is similar to making drip coffee. However, the pressure is the main difference.

The Head of the Group

The group head is the portafilter you put in when making espresso. It disperses water in the portafilter, and then regulates the pressure during the extraction. There are a variety of group heads each with their own advantages and drawbacks. Some focus on temperature stability, others on pre-infusion features, and others are designed to control the lever. Some have a combination, such as the E61. This is a favorite among baristas as it provides a variety of advantages in a single package.

As you can see in the above photo the head of the group is equipped with several notches. You place your portafilter into these notches and turn the head around to secure it. There is also a rubber gasket in the notches, which helps create an airtight seal when you insert your portafilter into the machine. The notches on the head allow for a precise position of the portafilter which is essential to ensure an even extraction.

In addition to allowing you to effortlessly insert your portafilter the group head is responsible for maintaining a consistent temperature. It does this by circulating hot water through the brew basket and around the portafilter to ensure that it's always at the right temperature for extraction. This is important because even a few degrees can mean the difference between excellent and great espresso.

The Pump

Motorized pumps in espresso machines that rotate provide the nine atmospheric bars of pressure required for espresso extraction. This is different from manual piston machines that rely on levers. This pressure builds up by removing tap water from a reservoir, and pumping it through a heat exchanger prior being pushed through the ground coffee inside the group head.

Pumps are generally less expensive than piston-driven machines, and tend to last longer, [Redirect-302] however both types of machines could degrade with overuse and insufficient cleaning. Pumps are also more complicated mechanically, and can add to the price of even the most basic models.

Some espresso machines employ steam pressure instead of a pump for brewing espresso. The disadvantage of this is that the same boiler that produces steam also increases the temperature of water until it reaches boiling which could lead to excessive extraction. They also have to constantly rebuild their pressure in between cups. This requires energy and time.

Many espresso machines utilize a vibration or rotary pump, which has a vibration model using a vibrating disc to create pressure and rotating models that push hot water through the grounds under high speed. Both types of machines can make excellent espresso, but the rotary pumps are quieter, and more durable than vibration pumps.

The Boiler

The boiler is what heats the water to the ideal temperature to extract. The resulting steam is then transferred to the portafilter containing the ground espresso and is then pumped down into the cup. During this process the steam creates enough pressure to push the grounds of the coffee through. This creates a layer crema on top. This is one of the main characteristics of a good espresso.

There are three distinct types of espresso machines, each having different pumps and the temperature of the brew. There are a variety of ways to control the amount of brew, as well as 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 both steam and brew however the pressure they were able to create was minimal - two bars of atmospheric pressure at the most. This led to the coffee tasting burnt and bitter. This is why the Milanese manufacturers Luigi Bezzerra and Desiderio Pavoni invented the modern espresso machine.

The most commonly used espresso machine is a semiautomatic that has an electric pump. These are the images people have when they think of an retro espresso machine maker. Semi-automatic machines require you to grind and tamp the beans on your own while the pump controls the flow of water and pressure. This is a great solution that combines human control with mechanized consistency.

The Filter

Typically, espresso machines have filters that separate the grounds of the coffee as they go through the hot water. The filter is also an essential part of the machine's temperature control, since it helps to prevent overheating.

A filter can also help with flavor since it allows for an extended flowering time. This lets the beans let their nuances out, and also allows for better extraction.

However, it is important to remember that even a great filter can produce a bad cup of coffee, since the quality of the beans and extraction are crucial.

This is where the magic happens, it's the thing that makes espresso taste good. The grouphead, often referred to as the brew head, is where the portafilter (the thingy you put the ground coffee in) is located when you're making espresso.

In the steam-driven espresso machine hot water is heated in an airtight tank to create steam. Steam then pushes the hot water through the grounds at a high pressure. These machines are cheaper and easier to maintain than pumps-driven models. However, they are not as efficient in their ability to create the ideal brewing conditions, because 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 been gaining popularity. They use an air compressor to push the hot water through the grounds and are significantly more portable than electric steam-driven machines.