How Does Machine Espresso Work?
Machine espresso utilizes precise pressure and mind-blowing filter technology to make the coffee we love. How exactly does it work?
To make an espresso hot water is pushed under pressure through finely ground coffee. The process is similar to making drip coffee, however the main difference lies in the pressure.
The Head of the Group
As the name implies the group head is where you insert your portafilter when making espresso. It is responsible for dispersing the water into the portafilter and then controlling the pressure of the resulting extraction. There are many different kinds of group head, each with their particular advantages and disadvantages. Some are focused on temperature stability, some on pre-infusion options, and others are designed to control the lever. Some come with a combination of both, such as the E61. This is a very popular choice for baristas as it provides a variety of advantages in a single package.
As you can see from the photo above the group head is fitted with several notches. You can place your portafilter into these notches and twist the head to lock it. A gasket of rubber is situated within the notches to create a seal as you insert your portafilter. The notches on the head allow for an exact position of the portafilter which is vital for a consistent extraction.
The group head not only lets you to insert your portafilter easily however it also keeps the temperature at a constant level. This is accomplished by cycling hot water around the portafilter and through the brew basin, ensuring that the temperature is always at the right level to extract the coffee. This is important because just a few degrees could make the difference between good and excellent espresso.
The Pump
In contrast to manual piston machines which rely on a lever that pressurize water, the rotary espresso machines use motorized pumps to deliver the nine atmospheric bars of pressure necessary for espresso extraction. The pressure builds by drawing tap water from a reservoir, and pumping it through a heat exchanger before being shot through the ground coffee in the group head.
Pumps are generally less expensive than piston-driven models, and they tend to last longer. However, both types of machines may degrade with overuse and insufficient cleaning. commercial espresso machine are also more complex mechanically, and can add to the price of even the simpler models.
Some espresso machines use steam pressure instead of a pump to make espresso. This can result in over-extraction because the boiler that makes steam also warms the water to boil. Additionally, these machines frequently have to restore their pressure between cups, which requires time and energy.
A majority of espresso machines use a vibration or rotary pump, with a vibration model using a vibrating disc to create the pressure and an rotary model that pushes hot water through the grounds at high speed. Both machines produce great espresso however rotary machines tend to be more quiet, durable and less likely to break down.
The Boiler
The boiler is the component which heats the water to the optimal temperature for extraction. The steam created gets to the portafilter which contains the espresso coffee grounds. It is then funneled into the cup. During this process, the steam creates pressure and pushes through the grounds of the coffee. This results in a whipped-up the top of the espresso. This is one of the main characteristics of a great espresso.
There are three types of espresso machines, each having different types of pumps and the temperature of the brew. There are a variety of ways to control the strength of the brew and the size of cup that can be made by the machine.
The first espresso machines were steam-type. They had one boiler to make both brew and steam, however, the pressure they could create was minimal - two bars of atmospheric pressure at the most. This resulted in the coffee tasting bitter and burnt. The modern espresso machine was designed by the Milanese manufacturers Luigi Bezzerra & Desiderio Pavoni.
The most popular espresso machine is a semiautomatic one with an electric pump. When people think of espresso machines, they envision these machines. If you have a semi-automatic machine you have to grind the beans and tamp them by hand. The pump provides regulated water flow and pressure. This is a great compromise between the human touch and the mechanized accuracy.
The Filter
Typically, espresso machines employ a filter to separate out the grounds of the coffee as they go through the hot water. The filter is also a vital element of the machine's temperature control, as it helps prevent overheating.
It also helps with flavor, since a filter lets you enjoy a longer bloom phase. This lets the beans let their nuances out, and allows for a better extraction.
It is important to remember that even the most efficient filter can produce a bad cup of coffee. The quality of the beans and the extraction, remain crucial.
This is where the magic happens, it's what makes espresso taste good. The grouphead (also called the brewhead) is where you put the portafilter - the thingy which you put the coffee grounds in, when making espresso.
Steam-driven espresso machines use hot water that is heated in an airtight container to make steam. The steam then pushes hot water through grounds of coffee under high pressure. These machines are cheaper and are easier for the user to maintain than pumps-driven models. However, they are not as efficient in their ability to produce the perfect conditions for brewing, since they operate at 1-1.5 bars of pressure. However, the perfect shot requires 9-10 bar.
In recent years, compressed air pump-driven espresso machines have been gaining popularity. They utilize an air compressor to force hot water through grounds, and are far more portable than steam-driven electric machines.