How Does Machine Espresso Work?
The machine espresso uses precise pressure and filter technology that is awe-inspiring to create the coffee you enjoy. How does it work exactly?
Espresso is created by forcing hot water under high pressure through finely ground coffee. The process is similar to that of making drip coffee. However, the pressure is the major difference.
The Head of the Group
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 numerous kinds of group heads, each with its own advantages and disadvantages. Some focus on temperature stability, some on pre-infusion options, and others are designed to control the lever. There are even some that include a mix of features, like the E61 one, which is the most popular choice among baristas for its ability to offer multiple perks in one package.
As you can see in the above photo the group head is made up of several notches to put your portafilter, then twist it manually to lock it in. A rubber gasket is located inside the notches to help create a seal as you insert your portafilter. The notches allow for precise placement of the portafilter. This is crucial to ensure a consistent extraction.
Aside from allowing you to effortlessly insert your portafilter 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 constant for extraction. This is important because just a few degrees could be the difference between a good and great espresso.
The Pump
The motorized pumps in espresso machines rotary provide nine atmospheric bar pressure needed for espresso extraction. This differs from manually operated piston machines that employ levers. The pressure builds up by removing tap water from a reservoir, and pumping it through a heat exchanger before being pushed through the ground coffee in the group head.
Pumps tend to be cheaper than piston-driven models, and they tend to last longer, but both types of machine can degrade with overuse and insufficient cleaning. Pumps are also more complex mechanically, which can increase the cost of even simpler models.
Certain espresso machines eliminate the pump completely and instead use steam pressure to brew espresso. This can result in over-extraction because the boiler that produces steam also warms the water to boil. In addition, these machines frequently have to rebuild their pressure between cups, which takes time and energy.
Many espresso machines make use of a vibration or rotary pump, which is a vibration model using a vibrating disc that generates the pressure and rotating models that push hot water through the grounds at high speed. Both machines can make great espresso but rotary machines are more quiet, durable and less likely to fail.
The Boiler
The boiler is what makes the water warm to the ideal temperature for extraction. The steam that is produced reaches the portafilter, which contains the ground espresso coffee, and is then pumped down into the cup. The steam creates enough pressure to push the coffee grounds through. This results in a layer crema on top. This is one of the hallmarks of a good espresso.
There are three types of espresso machines, each with a different type of pump and brew temperature. There are a variety of ways to control the brew and the size of cup that can be produced by the machine.
The first espresso machines were steam-based. They employed one boiler to create both steam and brew but the pressure they could create was minimal - two bars of atmospheric pressure at most. This led to the coffee tasting burnt and bitter. This is the reason why Milanese manufacturers Luigi Bezzerra and Desiderio Pavoni invented the modern espresso machine.
The most popular espresso maker is a semi-automatic one that has an electric pump. This is what people envision when they think of an espresso machine. With a semi-automatic machine, you grind the beans and then tamp them by hand, but the pump is able to regulate the flow of water and pressure. This is a great compromise between the human touch and the here mechanised consistency.
The Filter
Espresso machines typically have a filter that separates the coffee grounds from the hot water. The filter is also a vital element of the temperature control system as it prevents the machine from overheating.
A filter also improves flavor because it allows for the beans to flower for a longer period of time. This allows the beans to release their flavor and gives the chance 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, are still very important.
This is where the magic happens. It's what makes an espresso really taste great. The grouphead, sometimes called the brew head, is where the portafilter (the device you put the ground coffee in) is placed when making espresso.
Steam-driven espresso machines make use of hot water heated in an airtight container to produce steam. The steam then moves hot water through the coffee grounds under high pressure. These kinds of machines are generally less expensive and easier to maintain than pumps-driven models. However, they are not as efficient in their ability to create the perfect conditions for brewing, because they operate at 1-1.5 bars of pressure. The perfect shot requires 9-10 bar.
In recent years, compressed air-driven espresso machines have become more popular. They use an air compressor to force hot water through grounds and are much more portable than steam-driven electric machines.