How Does Machine Espresso Work?
Machine espresso utilizes precise pressure and incredible filter technology to produce the coffee we love. But how exactly does it work?
To make an espresso hot water is forced under high pressure through finely ground coffee. The process is similar to making drip coffee but the key difference is in the pressure.
The Group Head
The group head is the portafilter that you put in when making espresso. It distributes water into the portafilter, and regulates the pressure of extraction. There are numerous kinds of group heads each with its own advantages and disadvantages. Some are designed for stability in temperature, while others are specifically designed to handle pre-infusion. Others are made to control the lever. There are also some that come with a range of features, such as the E61, which is the classic choice among many baristas because of its ability to offer multiple perks in a single package.
As you can see in the photo above the head of the group is equipped with several notches. It is possible to place your portafilter in these notches, then turn the head around to secure it. There is also a gasket made of rubber that resides inside the notches and helps create the seal when you insert your portafilter into the machine. The notches allow for precise placement of your portafilter. This is vital for an efficient extraction.
The group head does not just allow you to place your portafilter easily, but it also maintains the temperature at a constant level. This is accomplished by cycling hot water around the portafilter and through the brew-basket to ensure that the temperature is always at the right level for extraction. This is important because just a few degrees could be the difference between a excellent and great espresso.
The Pump
The motorized pumps used in rotary espresso machines supply the nine atmospheric bar pressure required for espresso extraction. This is different from manually operated piston machines that employ a lever. The pressure builds up by removing tap water from a reservoir, and pumping it through a heat exchanger prior to being pumped through the ground coffee in the group head.
Pumps are generally less expensive and last for longer than piston-driven machines. However, both kinds of machines may degrade due to excessive use and poor cleaning. Pumps are also more complex mechanically, and can add to the cost of even most basic models.
Some espresso machines make use of steam pressure instead of a pump for brewing espresso. This can cause over-extraction because the boiler that makes steam also causes the water to boil. They also have to constantly rebuild their pressure in between cups. This requires energy and time.
A majority of espresso machines utilize either a vibration or rotary pump. A vibration model makes use of an oscillating disk to create pressure, whereas a rotating model pushes hot water through the ground at high speed. Both machines can make great espresso, but rotary machines are more stable, quieter and less likely to fail.
The Boiler
The boiler is what heats the water to the right temperature for extraction. The resultant steam then reaches the portafilter that contains the ground espresso coffee and is then funneled down into the cup. During this process, steam creates pressure to push 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, and they differ in the kind of pump they use and how hot the brew is. There are various ways to control the brew and the size of the cup that can be made by the machine.
The first espresso machines were steam-based. The first espresso machines were steam types. This led to the coffee tasting burnt and bitter. The modern espresso machine was developed by the Milanese manufacturers Luigi Bezzerra & Desiderio Pavoni.
The most commonly used espresso machine is a semiautomatic one 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 The pump, however, regulates the water flow and pressure. This is an excellent compromise between human touch and the mechanized quality.
The Filter
Typically, espresso machines have filters to separate the grounds of coffee when they pass through the hot water. The filter is also a vital part of the temperature control system, because it stops the machine from overheating.
It also aids in flavor, as a filter allows for a more prolonged bloom phase. This helps the beans to release their flavor and gives an opportunity for better extraction.
It is important to keep in mind that even the finest filter can produce a bad coffeee machines cup of coffee. The quality of the beans and the extraction, remain vital.
This is where the magic happens, it's the thing that makes espresso taste good. The grouphead (also known as the brewhead) is where you place the portafilter, the thingy that you use to put the coffee grounds in, when making espresso.
In a steam-driven espresso machine, hot water is heated in an airtight tank to create steam. This is then pushed through the grounds under high pressure. These types of machines are usually cheaper and easier to maintain than pumps-driven models. However, they are limited in their capacity to create the perfect brewing conditions as they only operate at 1-1.5 bars of pressure. However, the perfect shot requires 9-10 bars.
In recent years, compressed air-driven espresso machines have been gaining popularity. They utilize an air compressor to push hot water through the grounds, and are far more portable than electric steam-driven machines.