How Does Machine Espresso Work?
Machine espresso uses precision pressure and mind-blowing filter technology to make the perfect cup of coffee. What 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. However, it is the pressure that makes the main difference.
The Group Head
The group head is the portafilter that you place in the espresso maker when making it. It is responsible for dispersing the water into the portafilter before controlling the pressure of the extraction. There are a variety of types of group head each with its particular advantages and disadvantages. Some are designed to provide stability of temperature while others are specifically designed to handle pre-infusion. Some are designed to control the lever. Some come with a range of features, such as the E61 one, which is the most popular choice among baristas due to its capacity to provide multiple benefits in a single package.
As you can see from the above photo, the group head is fitted with several notches. It is possible to place your portafilter inside these notches, and then twist the head to lock it. A gasket made of rubber is placed inside the notches to help create a seal while you insert your portafilter. The notches permit an exact placement of the portafilter. This is crucial for an efficient extraction.
The group head not only lets you to insert your portafilter easily, but it also maintains a constant temperature. It does this by cycling hot water through the brew basket and around the portafilter to ensure that it is always at the correct temperature for extraction. This is crucial, since even a few degrees can be the difference between a excellent and great espresso.
The Pump
Unlike manual piston machines, that use a lever to pressurize water, the rotary espresso machines use motorized pumps that provide the nine atmospheric bars of pressure needed for espresso extraction. The pressure is built by pumping water through a heat-exchanger and then through the ground coffee.
Pumps are typically less expensive and last for longer than piston-driven machines. However, both types of machines can deteriorate because of excessive use and inadequate cleaning. Pumps are also more complex mechanically, and can add to the cost of even most basic models.
Some espresso machines use steam pressure instead of a pump to brew espresso. This can cause over-extraction because the boiler that produces steam also warms the water to boil. These machines also have to continuously rebuild their pressure between cups. This requires energy and time.
A large majority of espresso machines employ an rotary or a vibration pump. A vibration model uses a vibrating disk to generate pressure, whereas a Rotary model pushes hot coffee through the ground at a fast speed. Both machines can make excellent espresso, however rotary machines are quieter, more durable and less likely to break.
The Boiler
The boiler is the component that heats water to the optimal temperature to extract. The resulting steam is then transferred to the portafilter which holds the ground espresso coffee, and is then pumped down into the cup. During this process, the steam causes pressure to push through the coffee grounds. This creates a crema on top of the espresso. This is the hallmark of a great espresso.
There are three kinds of espresso makers, which differ in the type of pump they use and the degree of heat that the espresso is. There are also different ways that the brew can be controlled as well as the size of the cup that the machine is capable of making.
The earliest espresso machines were steam-based. They used one boiler to make both brew and steam, however the pressure they were able to produce was very low - just two bars of atmospheric pressure at the most. This led to the coffee tasting burnt and bitter. The modern espresso machine was designed by the Milanese producers Luigi Bezzerra & Desiderio Pavoni.
The most commonly used espresso machine is a semiautomatic model with an electric pump. These are the images people have when they think of an espresso machine. Semi-automatic machines require you to grind and tamp the beans on your own however the pump controls the flow of water and pressure. This is a great compromise between the human touch and mechanized accuracy.
The Filter
Espresso machines usually have a filter that separates the grounds of coffee from hot water. The filter is also an essential element of the machine's temperature control, as it helps prevent overheating.
Filters also aid in flavor because it allows for the beans to flower for a longer period of time. This allows the beans to release their flavor and allows for better extraction.
It is important to remember that even the best filter can produce a bad cup of coffee. The quality of the beans, and the extraction process remain vital.
This is where the magic happens, it's the thing that makes an espresso really taste good. The grouphead, also referred to as the brewhead, is where the portafilter (the thingy you put the coffee grounds 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 coffee under high pressure. These kinds of machines are typically cheaper and easier to maintain than pump-driven models. However, they are not as efficient in their capacity to create the ideal brewing conditions, as they only operate at 1-1.5 bars of pressure, while the perfect shot requires 9-10 bars.
In recent years, compressed air-pump-driven espresso machines have become more popular. They utilize an air compressor to force the hot water through the grounds and are significantly more portable than electric steam-driven machines.