How Does Machine Espresso Work?
Machine espresso makes use of precise pressure and mind-blowing filter technology to make the coffee we love. How exactly does it work?
Espresso is made by pushing hot water under high pressure through finely ground coffee. The process is similar to that of making drip coffee. However the pressure is the main difference.
The Group Head
The group head is the portafilter that you insert when brewing espresso. It distributes water into the portafilter, and then regulates the pressure of extraction. There are several different types of group head each with its unique advantages and disadvantages. Some are designed for the stability of temperature while some are built to handle pre-infusion. Others are made to control the lever. There are some that have a combination of features, such as the E61 that is the classic choice among many baristas due to its ability to provide multiple benefits in one package.
As you can see in the picture above the group head is fitted with several notches. You place your portafilter inside these notches, and then twist the head to secure it. A gasket made of rubber is placed 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 efficient extraction.
Apart from allowing you easily place your portafilter in, the group head is responsible for maintaining an even temperature. This is achieved by cycling hot water around the portafilter and through the brew basin, ensuring that the temperature is at the right level to extract the coffee. It is important to remember that even a small difference can make the difference between a great and a great espresso.
The Pump
The motorized pumps that are used in rotary espresso machines supply the nine atmospheric bars of pressure required for espresso extraction. This differs from manual piston machines which use levers. The pressure builds up by drawing tap water from a reservoir and pumping it through a heat exchanger prior being shot through the ground coffee inside the group head.
Pumps are typically less expensive than piston-driven machines and tend to last longer, although both types of machine can be damaged by excessive use and inadequate cleaning. They also increase the complexity of mechanical systems and can lead to the cost of even the simplest models.
Certain espresso machines eliminate the pump entirely and utilize steam pressure to make espresso. This can result in over-extraction because the boiler that produces steam also heats the water until it comes to a boil. In addition these machines typically have to rebuild their pressure between cups, which takes time and energy.
A majority of espresso machines use a vibration or rotary pump, with a vibrating model using a vibrating disc to create the pressure, and a rotary model pushing hot water through the grounds at high speed. Both types of machines can make excellent espresso, however the rotary pumps are quieter, and more durable than vibration pumps.
The Boiler
The boiler is the part that heats water to an optimal temperature for extraction. The steam that is created is then directed 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 creates a layer crema that is then poured over. This is the hallmark of a good espresso.
There are three kinds of espresso makers, and they differ in the kind of pump they use and the degree of heat that the coffee is. There are various ways in which the brew can be controlled as well as the dimensions of the cup the machine can produce.
The first espresso machines were steam-types. They utilized only one boiler to make steam and brew, but the pressure they could generate was low - only two bars of atmospheric pressure at the most. The coffee tasted bitter and burned. The modern espresso machine was created by the Milanese manufacturers Luigi Bezzerra & Desiderio Pavoni.
The most common espresso machine is a semiautomatic model with an electric pump. When people think of espresso machines, they think of these machines. With a semi-automatic espresso machine, you grind the beans and tamp them by hand. The pump provides regulated water flow and pressure. This is a great combination of human control and mechanized reliability.
The Filter
Espresso machines usually use a filter that separates the coffee grounds from the hot water. The filter is also a vital part of the machine's temperature control, since it stops overheating.
A filter can also help with flavor, as it permits a longer flowering phase. This allows the beans to release their flavors, and allows for better extraction.
It is important to keep in mind that even the most efficient 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, and it's what makes an espresso really taste good. The grouphead (also known as the brewhead) is where you place the portafilter, the device used to place the coffee grounds in, when making espresso.
espresso coffee machines -driven espresso machines make use of hot water that is heated in an airtight container to make steam. The steam then pushes hot water through the grounds of coffee under high pressure. These types of machines are typically cheaper and easier to maintain than pump-driven models. However, they are not as efficient in their ability to produce the ideal brewing conditions, because they operate at 1-1.5 bars of pressure. However, the perfect shot requires 9-10 bars.
In recent years, espresso machines driven by compressed air-pump have become increasingly popular. They make use of an air compressor to force hot water through the ground. They are also more mobile than steam-driven electric espresso machines.