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How Does Machine Espresso Work? The machine espresso utilizes precision pressure, and filtering system that is awe-inspiring to make the coffee you enjoy. But how exactly does it work? In order to make espresso, hot water is pushed under pressure through finely ground coffee. The process is similar to making drip coffee but the difference is in the pressure. The Group Head As the name implies, the group head is where you put your portafilter in when making espresso. It disperses water into the portafilter, and controls the pressure of the extraction. There are several different types of group heads each with its distinct advantages and disadvantages. Some are specifically designed for stability of temperature while others are designed to handle pre-infusion. Others are built to control the lever. Some contain a variety of features, like the E61 one, which is the classic choice among many baristas due to its ability to offer multiple perks in a single package. As you can see in the above photo the head of the group has a number of notches. It is possible to place your portafilter inside these notches, and then turn the head around to secure it. A rubber gasket is located inside the notches, which helps create a seal as you insert your portafilter. The notches on the head permit a precise location of the portafilter which is necessary for a consistent extraction. In addition to allowing you to easily place your portafilter in, the group head is responsible to maintain an even temperature. It does this by cycling hot water through the brew container and around the portafilter, ensuring that it's always at the correct temperature for extraction. This is vital, because even a small difference in temperature can be the difference between a good and excellent espresso. The Pump In contrast to manual piston machines that use a lever to pressurize water, rotary espresso machines rely on motorized pumps to provide the nine atmospheric bars of pressure needed for espresso extraction. This pressure is built up by pumping water through a heat-exchanger and then through the ground coffee. Pumps tend to be more affordable and last longer than piston-driven machines. However, both kinds of machines may degrade due to overuse and insufficient cleaning. Pumps are also more complicated mechanically, which can increase the price of even the simple models. Certain espresso machines do away with the pump entirely and employ steam pressure to create espresso. This can result in over-extraction because the boiler that produces steam also causes the water to boil. They also have to continually rebuild their pressure between cups. This requires energy and time. www.coffeee.uk make use of 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 tend to be quieter, more durable and less likely to break. The Boiler The boiler is the part that heats the water to the optimal temperature to extract. The resulting steam is then transferred to the portafilter which holds ground espresso beans and gets funnelled down into the cup. In this process, the steam causes pressure to push through the coffee grounds. This results in a crema on top of the espresso. This is one of the main characteristics of a good espresso. There are three kinds of espresso makers. They differ in the kind of pump they use and how hot the coffee is. There are various ways to control the brew as well as the size of cup that can be produced by the machine. The first espresso machines were steam types. They had only one boiler to make both brew and steam, but the pressure they could create was minimal – two bars of atmospheric pressure at the most. This resulted in the coffee tasting burnt and bitter. The modern espresso machine was invented by the Milanese manufacturers Luigi Bezzerra & Desiderio Pavoni. The most popular espresso maker is a semi-automatic one with an electric pump. This is what people envision when they think of an espresso maker. Semi-automatic machines require you to grind and tamp the beans yourself however the pump controls the flow of water and pressure. This is a great compromise between the human touch and the mechanized quality. The Filter Typically, espresso machines use filters that separate the grounds of the coffee as they go through the hot water. The filter is also an essential part of the machine's temperature control, as it helps prevent overheating. It also improves flavor, since a filter allows for a more prolonged bloom time. This lets the beans release their flavor and improves extraction. However, it is important to remember that even a great filter can produce a bad cup of coffee, since the quality of the beans and extraction is vital. This is where the magic happens, it's the thing that makes an espresso really taste great. The grouphead, often called the brew head, is where the portafilter (the thingy you put the coffee ground into) is located when you're making espresso. In a steam-driven espresso machine, hot water is heated in an airtight tank to create steam. This then pushes the hot water through the grounds at a high pressure. These kinds of machines are usually less expensive and easier to maintain than pump-driven models. They are however limited in their ability to create the ideal brewing conditions as they only operate with 1-1.5 bar of pressure. The ideal shot requires 9-10 bars. In recent years, compressed air-driven espresso machines have become more popular. They utilize an air compressor to force hot water into the ground and are more mobile than steam-driven electric espresso machines.