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How Does Machine Espresso Work?

Machine espresso uses precision pressure and amazing filter technology to make the coffee we love. What exactly does it work?

Espresso is created by forcing hot water under 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 that you place in the espresso maker when making it. It distributes water into the portafilter, and regulates the pressure of extraction. There are a variety of types of group head, each with their particular advantages and drawbacks. Some are specifically designed for stability in temperature, while others are specifically designed to handle pre-infusion. Others are made to control the lever. Some contain a variety of features, like the E61, which is to be the most popular among baristas for its ability to offer multiple perks in one package.

As you can see in the above photo the group head has a number of notches. You place your portafilter in these notches and then twist the head to secure it. A gasket of rubber is situated within the notches to create a seal as you insert your portafilter. The notches on the head permit an exact location of the portafilter which is necessary for a consistent extraction.

Apart from allowing you effortlessly insert your portafilter the group head is responsible to ensure that the temperature remains even. This is achieved by cycling hot water around the portafilter, and through the brew-basket, ensuring that the temperature is at the right level for extraction. It is important to note that even a few degree variation can mean the difference between a great and a great espresso.

The Pump

The motorized pumps that are used in rotary espresso machines supply the nine atmospheric bar pressure that is required for espresso extraction. This differs from manually operated piston machines that employ a lever. This pressure is built up by pumping water through a heat-exchanger and then through the ground coffee.

Pumps are typically less expensive than piston-driven machines and tend to last longer. However, both types of machines can be damaged by excessive use and inadequate cleaning. Pumps are also more complex mechanically, which can increase the cost of even the simple models.

Certain espresso machines remove the pump completely and make use of steam pressure to make espresso. The downside is that the same boiler that produces steam also increases the temperature of water to the point of boiling which could lead to over-extraction. The machines also need to constantly rebuild their pressure in between cups. This takes energy and time.

Many espresso machines make use of either a rotary or vibration pump, with a vibration model using a rotating disc to generate the pressure and the rotary model pushing hot water through the grounds under high speed. Both machines can make excellent espresso but rotary machines are quieter, more durable and less likely to break down.

The Boiler

The boiler is the component that heats water to the optimal temperature for extraction. The resulting steam is then transferred to the portafilter containing ground espresso beans and is then pumped into the cup. During this process the steam is able to create enough pressure to push the grounds of coffee through. This results in a layer of crema that is then poured over. This is the hallmark of a good espresso.

There are three kinds of espresso machines, each with different types of pumps and the temperature of the brew. There are also different ways in which the brew can be controlled and the size of the cup that the machine can make.

The first espresso machines were steam type. They had a single boiler to make steam and brew, but the pressure they could generate was low - only two bars of atmospheric pressure at most. The coffee tasted bitter and burned. The modern espresso machine was invented by the Milanese producers Luigi Bezzerra & Desiderio Pavoni.

The most popular espresso maker is a semi-automatic one with an electric pump. When people think of espresso machine black friday machines, they envision these machines. Semi-automatic machines require you to grind and tamp the beans yourself however the pump controls the flow of water and pressure. This is a great compromise between the human touch and mechanized quality espresso machine.

The Filter

Espresso machines usually use filters that separate the grounds of coffee from hot water. The filter is also an essential part of the machine's temperature control, since it stops overheating.

A filter also improves flavor, as it permits a longer flowering period. This lets the beans release their flavors, and improves extraction.

It is important to remember that even the best espresso machine filter can make a bad cup of coffee. The quality of the beans and the extraction, are still crucial.

It's in this area that the magic takes place. This is what makes espresso taste so delicious. The grouphead, sometimes referred to as the brewhead, is where the portafilter (the thing you put the ground coffee into) is placed when you're making espresso.

Steam-driven espresso machines use hot water heated in an airtight container to create steam. The steam then pushes hot water into the grounds of the coffee under pressure. These machines are cheaper and easier for the owner to maintain than pumps-driven models. They are however limited to create the ideal conditions for brewing as they only operate with 1-1.5 bar of pressure. The perfect shot requires 9-10 bars.

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