How Does Machine Espresso Work?
Machine espresso uses precision pressure and incredible filter technology to produce the coffee we love. How exactly does it work?
Espresso is created by forcing hot water under high pressure through finely ground coffee. The process is similar to making drip coffee, but the difference is in the pressure.
The Head of the Group
As the name suggests the group head is where you place your portafilter when brewing espresso. It disperses the water into the portafilter, and controls the pressure of the extraction. There are many different types of group heads, each with its own advantages and disadvantages. Some focus on temperature stability, whereas others on pre-infusion capabilities, while others are designed to control the lever. There are also some that include a mix of features, such as the E61 that is the standard choice for many baristas for its ability to offer multiple perks in a single package.
As you can see from the photo above the head of the group is equipped with several notches. The portafilter is placed inside these notches, and then turn the head around to secure it. A gasket made of rubber is positioned inside the notches to help create a seal when you insert your portafilter. The notches permit precise placement of the portafilter. This is vital for an accurate extraction.
Apart from allowing you effortlessly insert your portafilter the group head is responsible for maintaining an even temperature. This is done by cycling hot water around the portafilter, and through the brew-basket, making sure that the temperature is constant to extract the coffee. It is crucial to keep in mind that even a slight deviation can make the difference between a good and a great espresso.
The Pump
The motorized pumps used in rotary espresso machines provide the nine atmospheric bars of pressure required to extract espresso. This is different from manual piston machines which use levers. This pressure is generated by pumping water through a heat-exchanger and then through the ground coffee.
Pumps are generally cheaper and last longer than piston-driven machines. However, both types of machines are susceptible to degrading because of excessive use and insufficient cleaning. Pumps are also more complex mechanically, which can increase the price of even the simplest models.
Certain espresso machines can eliminate the pump entirely and use steam pressure to brew espresso. This can result in over-extraction because the boiler that produces steam also warms the water to boil. In addition these machines typically have to restore their pressure between cups, which takes time and energy.
A majority of espresso machines utilize the rotary or vibration pump. A vibration model utilizes the vibrating disk to create pressure, while the rotating model pushes hot water through the ground at a fast speed. Both machines can produce excellent espresso, but rotary machines are more quiet, durable and less likely to break down.
The Boiler
The boiler is what is used to heat the water to the ideal temperature for extraction. The resultant steam then reaches the portafilter that contains the ground espresso and is then funneled down into the cup. During this process the steam is able to create enough pressure to push the coffee grounds through. This creates a crema on the top of the espresso. 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 the degree of heat that the brew is. There are different ways that the brew can be controlled, as well as the size of the cup the machine is capable of making.
The first espresso machines were steam-types. The first website espresso machines were steam types. The coffee tasted bitter and burnt. The modern espresso machine was designed by the Milanese manufacturers Luigi Bezzerra & Desiderio Pavoni.
The most common espresso machine is a semiautomatic with an electric pump. This is what people envision when they imagine an espresso machine. Semi-automatic machines require you to grind and tamp the beans by yourself, but the pump regulates the water flow and pressure. This is an excellent compromise between human touch and the mechanized quality.
The Filter
Typically, espresso machines use a filter to separate out the grounds of the coffee as they go through the hot water. The filter is also a vital component of the machine's temp control, as it helps prevent overheating.
Filters also aid in flavor since it allows for a longer flowering period. This allows the beans to release their flavors, and allows for better extraction.
However, it is important to remember that even a great filter can produce a bad cup of coffee, since the quality of the beans and extraction is important.
This is where the magic happens, it's what makes espresso taste good. The grouphead, often referred to as the brew head, is the place where the portafilter (the device you put the coffee ground into) is placed when you're making espresso.
Steam-driven espresso machines use hot water that is heated in an airtight container to produce steam. The steam then pushes hot water into the grounds of the coffee under pressure. These kinds of machines tend to be less expensive and simpler to maintain than pumps-driven models. However, they are limited in their ability to create the perfect conditions for brewing, because they operate at 1-1.5 bars of pressure, while the perfect shot requires 9-10 bars.
In recent years, espresso machines powered by a compressed air pump have become increasingly popular. They use an air compressor to force hot water through grounds and are much more portable than electric steam-driven machines.