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A Provocative Rant About Machine Espresso
How Does Machine Espresso Work?

Coffeee UK employs precise pressure and incredible filter technology to produce the coffee we love. What exactly is it?

Espresso is made by forcing hot water at high pressure through finely ground coffee. The process is similar to that of making drip coffee. However the pressure is the primary difference.

The Group Head

The group head is the portafilter that is inserted when you are making espresso. It disperses water into the portafilter and regulates the pressure of the extraction. There are several different types of group heads each with its own advantages and disadvantages. Some are designed for temperature stability while others are specifically designed to handle pre-infusion. Others are made to control the lever. Some include a mix of features, such as the E61 that is the classic choice among many baristas because of its ability to offer multiple perks in a single package.

As you can see from the photo above, the group head is fitted with several notches. You place your portafilter inside these notches, and then twist the head to lock it. There is also a gasket made of 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 the precise placement of the portafilter. This is vital for an accurate extraction.

Apart from allowing you easily connect your portafilter, the group head is responsible to maintain an even temperature. This is accomplished by cycling hot water around the portafilter and through the brew-basket, ensuring that the temperature is at the right level to extract the coffee. This is vital, because even a few degrees can make the difference between good and excellent espresso.

The Pump

Contrary to manual piston machines which use a lever to pressurize water, the rotary espresso machines use motorized pumps to deliver the nine atmospheric bars of pressure that are required to extract espresso. 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 become damaged due to excessive use and poor cleaning. Pumps are also more complex mechanically, which could increase the price of even the simplest models.

Certain espresso machines do away with the pump completely and instead use steam pressure to brew espresso. The drawback of this is that the same boiler that produces steam also raises the temperature of the water until it reaches boiling which could lead to excessive extraction. In addition, these machines frequently have to restore their pressure between cups, which takes time and energy.

Many espresso machines employ either a rotary or vibration pump, which is a vibration model using a vibrating disc to create pressure, and a rotary model pushing hot water through the grounds at high speed. Both machines can produce excellent espresso however rotary machines tend to be more stable, quieter and less likely to break down.

The Boiler

The boiler is the one that makes the water warm to a temperature that is ideal for extraction. The steam that is produced reaches the portafilter containing the ground espresso coffee, and is then funneled down into the cup. During this process the steam is able to create enough pressure to push the grounds of coffee through. This creates a crema on the top of the espresso. This is one of the hallmarks of a good espresso.

There are three kinds of espresso machines, each with 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 produced by the machine.

The first espresso machines were steam-type. They employed only one boiler to make both steam and brew, however, the pressure they could create was minimal - two bars of atmospheric pressure at the most. This led to the coffee tasting bitter and burnt. This is the reason Milanese producers Luigi Bezzerra and Desiderio Pavoni invented the modern espresso machine.

The most commonly used espresso maker is a semi-automatic machine with an electric pump. When people think of espresso 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 human control and mechanised reliability.

The Filter

Typically, espresso machines utilize filters to separate the grounds of the coffee as they go through the hot water. The filter is also a vital part of the temperature control system, as it prevents the machine from overheating.

It also improves flavor as a filter can allow for a longer bloom time. This lets the beans let their nuances out, and improves extraction.

It is important to remember that even the finest filter can produce a bad cup of coffee. The quality of the beans, and the extraction process are still very important.

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

In a steam-driven espresso machine hot water is heated in an airtight tank to produce steam, which is then pushed through the grounds with high pressure. These machines are cheaper and easier to maintain than pumps-driven models. However, they are not as efficient in their ability to produce the perfect conditions for brewing, since they are only operating at 1-1.5 bars of pressure. While the perfect shot requires 9-10 bar.

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