How Does Machine Espresso Work?
The machine espresso is made using precision pressure, and a filter technology that is mind-blowing to create the coffee you love. How does it work exactly?
Espresso is made by pushing hot water under high 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
The group head is the portafilter you place in the espresso maker when making it. It is responsible for dispersing the water into the portafilter and then controlling the pressure that results from the extraction. There are many different types of group heads each with distinct advantages and disadvantages. Some are specifically designed for the stability of temperature while some are designed to handle pre-infusion. Others are built to control the lever. Some have a combination of features, such as the E61, which is the classic choice among many baristas due to its ability to offer multiple benefits in one package.
As you can see in the photo above the group head is fitted with several notches. It is possible to place your portafilter into these notches and twist the head to lock it. A gasket made of rubber is placed in the notches to create a seal as you insert your portafilter. The notches permit the precise placement of the portafilter. This is essential for a consistent extraction.
Apart from allowing you easily insert your portafilter, the group head is responsible to ensure that the temperature remains even. This is accomplished by cycling hot water around the portafilter and through the brew basin, ensuring that the temperature is constant for extraction. It is important to realize that even a tiny differences can make the distinction between a great and a great espresso.
The Pump
The motorized pumps used in espresso machines that rotate provide the nine atmospheric bar pressure that is required for espresso extraction. This differs from manual piston machines which use levers. The pressure builds by removing tap water from a reservoir, and pumping it through a heat exchanger prior to being pumped through the ground coffee inside the group head.
Pumps tend to be cheaper than piston-driven machines, and they tend to last longer, however both types of machines may be damaged by excessive use and inadequate cleaning. They also increase the complexity of mechanical systems, which can result in an expensive price for even the most basic models.
Certain espresso machines do away with the pump completely and employ steam pressure to create espresso. This can result in over-extraction because the boiler that makes steam also heats the water to boil. In addition the machines often have to rebuild their pressure between cups, which requires time and energy.
Many espresso machines employ either a rotary or vibration pump, which is a vibration model using a vibrating disc to generate the pressure and a rotary model pushing hot water through the grounds under high speed. Both types of machine are capable of producing excellent espresso, but rotary machines are quieter and more durable than vibration pumps.
The Boiler
The boiler is the component that heats the water to the optimal temperature for extraction. The steam created is then directed to the portafilter, which is a container for espresso grounds. The steam is then channeled into the cup. During this process, the steam creates pressure that pushes through the grounds of the coffee. This results in a layer crema that is then poured over. coffee and espresso maker is one of the hallmarks of a great espresso.
There are three different types of espresso machines, each having distinct pumps and the temperature of the brew. There are a variety of ways to control the brew and the size of the cup that can be produced by the machine.
The first espresso machines were steam-types. They had one boiler to make both steam and brew, however the pressure they were able to create was minimal - two bars of atmospheric pressure maximum. The coffee tasted bitter and burnt. The modern espresso machine was invented by the Milanese manufacturers Luigi Bezzerra & Desiderio Pavoni.
The most popular espresso maker is a semi-automatic machine with an electric pump. When people think of espresso machines, they picture these machines. Semi-automatic machines require you to grind and tamp your beans yourself, but the pump regulates the water flow and pressure. This is an excellent compromise between human touch and the mechanised quality.
The Filter
Espresso machines typically have a filter that separates the coffee grounds from the hot water. The filter is also a vital part of the machine's temperature control, as it prevents overheating.
A filter can also help with flavor, as it permits a longer flowering period. This lets the beans let their nuances out, and allows for better extraction.
It is important to remember that even the finest filter can make a bad cup of coffee. The quality of the beans, and the extraction process, are still very important.
This is where the magic happens. It's what makes espresso taste great. The grouphead, sometimes referred to as the brew head, is where the portafilter (the thing you put the coffee grounds into) sits when you're making espresso.
In a steam-driven espresso machine hot water is heated in an airtight tank to create steam, which then pushes the hot water through the grounds at high pressure. These machines are cheaper and easier for the owner to maintain than pumps-driven models. However, they are not as efficient in their ability to provide the perfect brewing conditions since they operate at 1-1.5 bars of pressure. While the perfect shot requires 9-10 bars.
In recent years, espresso machines driven by a compressed air compressor have become increasingly popular. They utilize an air compressor to force hot water through grounds, and are far more portable than electric steam-driven machines.