How Does Machine Espresso Work?
Machine espresso employs precise pressure and mind-blowing filter technology to make the coffee we love. What exactly is it that makes it work?
To make espresso hot water is forced under high pressure through finely ground coffee. The process is similar to making drip coffee, but the major difference is in the pressure.
The Head of the Group
The group head is the portafilter that you insert when brewing espresso. It distributes water into the portafilter and regulates the pressure during the extraction. There are several different types of group head each with its particular advantages and disadvantages. Some are specifically designed for stability of temperature while others are built to handle pre-infusion. Others are made to control the lever. Some have a combination, such as the E61. This is a favorite among baristas due to the fact that it has multiple benefits in a single package.
As you can see from the picture above the group head is equipped with several notches. You can place your portafilter inside these notches, and then turn the head around to secure it. There is also Coffeee that is a part of the notches and helps to create a seal when you insert your portafilter into the machine. The notches permit precise placement of the portafilter. This is vital for an efficient extraction.
Apart from allowing you easily place your portafilter in, the group head is also responsible for maintaining an even temperature. It does this by cycling hot water through the brew basket, and around the portafilter to ensure that it is always at the right temperature for extraction. It is important to remember that even a slight variation can mean the difference between a good and excellent espresso.
The Pump
In contrast to piston machines that are manually operated, which rely on a lever that pressurize water, the rotary espresso machines use motorized pumps to supply the nine atmospheric bars of pressure needed for espresso extraction. This pressure builds up by drawing tap water from a reservoir and pumping it through a heat exchanger prior to being shot through the ground coffee in the group head.
Pumps tend to be cheaper than piston-driven machines and tend to last longer, but both types of machine can get damaged through overuse and lack of cleaning. They also add mechanical complexity and can lead to costly prices for even the most basic models.
Some espresso machines use steam pressure instead of a pump in order to brew espresso. This can lead to over-extraction as the boiler that produces steam also causes the water to boil. The machines must also continuously rebuild their pressure between cups. This requires energy and time.
Many espresso machines utilize an rotary or vibrating pump, which has a vibration model that uses a vibrating disc that generates the pressure, and a rotary model pushing hot water through the grounds at high speed. Both types of machine can make a great espresso, but the rotary pumps are quieter, and more durable than vibration pumps.
The Boiler
The boiler heats the water to a temperature that is ideal for extraction. The resultant steam then reaches the portafilter which holds the ground espresso coffee and is then pumped into the cup. During this process, the steam creates pressure that pushes through the grounds of the coffee. This creates a foam on the top of the espresso. This is one of the hallmarks of a good espresso.
There are three kinds of espresso makers, which differ in the type of pump they employ and how hot the brew is. There are a variety of ways to control the strength of the brew and the size of the cup that can be made by the machine.
The first espresso machines were steam-type. The earliest espresso machines were steam types. This resulted in the coffee tasting burnt and bitter. This is why Milanese makers Luigi Bezzerra and Desiderio Pavoni developed the modern espresso machine.
The most well-known espresso machine is a semiautomatic model 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 by yourself however the pump controls the water flow and pressure. This is a great compromise between the human touch and the mechanized consistency.
The Filter
Espresso machines typically have filters that separate the grounds of the coffee from the hot water. The filter is also an essential element of the machine's temperature control, as it prevents overheating.
Filters also aid in flavor, as it permits the beans to flower for a longer period of time. This allows the beans to let their nuances out, and improves extraction.
However it is crucial to keep in mind that even a good filter could result in a bad cup of coffee, because the quality of the beans and extraction is vital.
It's in this area that the magic takes place. 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 coffee grounds into, when making espresso.
Steam-driven espresso machines use hot water that is heated inside an airtight vessel to create steam. The steam then pushes hot water through the coffee grounds under high pressure. They are less expensive and easier to maintain than pumps-driven models. They are however limited to create the perfect conditions for brewing as they only 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 been gaining popularity. They use an air compressor to force hot water through the grounds and are much more portable than electric steam-driven machines.