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How Does Machine Espresso Work?

Machine espresso uses precision pressure and mind-blowing filter technology to make the delicious coffee we enjoy. But how exactly does it work?

Espresso is created by forcing hot water under high 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 that you insert when brewing espresso. It disperses water in the portafilter, and then regulates the pressure of extraction. There are a variety of types of group head, each with their own advantages and drawbacks. Some are specifically designed for temperature stability while others are designed to handle pre-infusion. Others are made to control the lever. Some come with a range of features, like the E61, which is the classic choice among many baristas due to its capacity to provide multiple benefits in one package.

As you can see from the above photo the group head is equipped with several notches. The portafilter is placed in these notches and then twist the head to lock it. A rubber gasket is located inside the notches to help make a seal when you insert your portafilter. The notches on the head permit a precise positioning of the portafilter which is essential to ensure a consistent extraction.

The group head does not just allow you to put in your portafilter easily, but it also maintains a constant temperature. It does this by cycling hot water through the brew pan and around the portafilter, ensuring that it's always at the right temperature for extraction. This is important, as just a few degrees could make the difference between a good and great espresso.

The Pump

Motorized pumps in rotary espresso machines supply the nine atmospheric bar pressure that is required to extract espresso. This differs from manual piston machines which use levers. This pressure builds up by drawing tap water from a reservoir, and pumping it through a heat exchanger prior to it is shot through the ground coffee inside the group head.

Pumps are generally less expensive than piston-driven machines and tend to last longer, although both types of machines could be damaged by excessive use and inadequate cleaning. They also create mechanical complexity and can lead to costly prices for even the simplest models.

Certain espresso machines do away with the pump completely and instead employ steam pressure to create espresso. The downside is that the same boiler that produces steam also increases the temperature of the water to boiling, which can lead to over-extraction. Additionally the machines often have to rebuild their pressure between cups, which takes time and energy.

Many espresso machines make use of the rotary or vibration pump. A vibration model utilizes a vibrating disk to generate pressure, whereas a circular model pushes hot liquid through the ground at a rapid speed. Both machines can make great espresso, but rotary machines are quieter, more durable and less likely to break down.

The Boiler

The boiler heats the water to the perfect temperature to extract. The resultant steam then reaches the portafilter, which contains ground espresso beans and is then pumped into the cup. During this process, steam creates pressure and pushes through the grounds of the coffee. This results in a layer of crema that is then poured over. This is the hallmark of a great espresso coffee maker.

There are three distinct types of espresso machines, each having distinct pumps and the temperature of the brew. There are different ways that the brew can be controlled, as well as the dimensions of the cup the machine is capable of making.

The first espresso machines were steam-types. They used only one boiler to make both steam and brew but the pressure they could generate was low - only two bars of atmospheric pressure, at most. This led to the coffee tasting burnt and bitter. This is why Milanese producers Luigi Bezzerra and Desiderio Pavoni developed the modern espresso machine.

The most well-known espresso machine is a semiautomatic model with an electric pump. These are what people imagine when they imagine an espresso machine. Semi-automatic machines require you to grind and tamp the beans by yourself however the pump controls the water flow and pressure. This is a great compromise between the human touch and the mechanised quality.

The Filter

Morphy Richards Espresso Machine (Http://Www.Keeha.Co.Kr/Bbs/Board.Php?Bo_Table=Notice_En&Wr_Id=1007302) machines typically use a filter that separates the grounds of the coffee from hot water. The filter is also a vital element of the temperature control system, as it keeps the machine from overheating.

A filter can also help with flavor since it allows for a longer flowering period. This allows the beans to release their nuances, and improves extraction.

It is important to remember that even the finest filter can make a bad cup of coffee. The quality of the beans and the extraction process remain vital.

It's in this area that the magic happens. This is the reason why espresso tastes so delicious. The grouphead (also known as the brewhead) is where you place the portafilter, the thingy that you put the grounds of coffee into when making espresso.

Steam-driven espresso machines use hot water that is heated inside an airtight container to produce steam. The steam then moves hot water through the grounds of the coffee under pressure. These machines are cheaper and easier for the user to maintain than pumps-driven models. They are however limited to create the perfect 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 hot water through grounds and are much more portable than steam-driven electric machines.