How Does Machine Espresso Work?
Machine espresso utilizes precise pressure and mind-blowing filter technology to make the delicious coffee we enjoy. How exactly does it work?
Espresso is created by forcing hot water at high pressure through finely-ground coffee. best portable espresso maker is similar to that of making drip coffee. However it is the pressure that makes the main difference.
The Group Head
As the name suggests, the group head is where you put your portafilter in when making espresso. It is responsible for dispersing the water into the portafilter and then controlling the pressure of the extraction. There are numerous kinds of group heads each with their own advantages and drawbacks. Some are designed to provide stability of temperature while others are built to handle pre-infusion. Some are designed to control the lever. Some include a combination like the E61. This is a preferred choice for baristas since it provides multiple advantages in one package.
As you can see in the above photo the group head comes with several notches where you put your portafilter, then twist it with your hands to lock it in. A gasket made of rubber is placed within the notches to create a seal while you insert your portafilter. The notches permit the precise placement of the portafilter. This is vital for an efficient extraction.
The group head not only lets you to insert your portafilter easily however it also keeps the temperature at a constant level. It does this by circulating hot water through the brew container and around the portafilter, making sure that it's always at the correct temperature to extract. This is important, as even a few degrees can make the difference between a good and great espresso.
The Pump
Contrary to manual piston machines which rely on a lever that pressurize water, Rotary espresso machines rely on motorized pumps to supply the nine atmospheric bars of pressure that are required for espresso extraction. The pressure builds up by drawing tap water from a reservoir and pumping it through a heat exchanger prior to being pushed through the ground coffee inside the group head.
Pumps tend to be less expensive than piston-driven machines and tend to last longer. However, both types of machine can become damaged due to excessive use and poor cleaning. They also create mechanical complexity, which can result in a high price tag on even the simplest models.
Certain espresso machines utilize steam pressure instead of a pump in order to brew espresso. The drawback of this is that the same boiler that produces steam also raises the temperature of the water to the point of boiling which can cause over-extraction. Additionally the machines often have to rebuild their pressure between cups, which requires time and energy.
Many espresso machines make use of an rotary or a vibration pump. A vibration model employs a rotating disk to generate pressure, whereas a circular model pushes hot liquid through the ground at a fast 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 the element that heats water to an optimal temperature to extract. The resulting steam is then transferred to the portafilter which holds the ground espresso and is then pumped into the cup. The steam is able to create enough pressure to push the coffee grounds through. This produces a layer of crema that is then poured over. This is one of the hallmarks of a good espresso.
There are three types of espresso makers, and they differ in the type of pump they employ and how hot the brew is. There are a variety of ways to control the amount of brew, as well as the size of cup that can be produced by the machine.
The first espresso machines were steam-types. They utilized only one boiler to make both steam and brew, however the pressure they were able to produce was very low - just two bars of atmospheric pressure at the most. This led to the coffee tasting burnt and bitter. The modern espresso machine was created by the Milanese producers Luigi Bezzerra & Desiderio Pavoni.
The most commonly used espresso machine is a semiautomatic model with an electric pump. When people think of espresso machines, they think of these machines. Semi-automatic machines require you to grind and tamp the beans yourself however the pump controls the water flow and pressure. This is a great compromise between the human touch and mechanized accuracy.
The Filter
Espresso machines typically use a filter that separates the grounds of the coffee from hot water. The filter is also a vital part of the machine's temperature control, as it prevents overheating.
It also helps with flavor as a filter allows for a more prolonged bloom phase. This allows the beans to let their nuances out and provides an opportunity for better extraction.
It is important to remember that even the finest filter could result in a poor cup of coffee. The quality of the beans, as well as the extraction, are still very important.
It's here that the magic takes place. This is the reason why espresso tastes so good. The grouphead (also called the brewhead) is where you put the portafilter, the thingy which you put the grounds of coffee into when making espresso.
In an espresso machine that is driven by steam, hot water is heated in an airtight tank to produce steam, which then pushes the hot water through the grounds at a high pressure. These types of machines are generally less expensive and simpler to maintain than pump-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, espresso machines driven by compressed air-pump are becoming increasingly popular. They make use of an air compressor to force hot water into the ground, and are more mobile than electric steam-driven espresso machines.