We recently talked to you about the history of the espresso machine , which became what we all know today after a series of improvements made by inventors and industrialists. If today espresso has that inimitable and immediately recognizable taste, we owe it to the experimentation that has followed over time.
So what are the steps of the espresso extraction process and how does a modern bar coffee machine work? Let’s find out!
The espresso coffee extraction process
Before we start talking about how the bar espresso machine works, let’s take a look at the steps that lead up to the coffee extraction. First of all, the roasted coffee is ground, dosed out and compacted in the portafilter, which is then attached to the dispenser head of the machine: inside this, the fundamental phases of pre-infusion and extraction of the drink take place.
When the barista presses the dispense button, the electrical pump increases the pressure of the water which is drawn directly from the main water network, and then sends it to the dispenser head via the heat exchanger. Once the hot water arrives here, thanks to the shower filter of the group it is distributed evenly over the block of compacted ground coffee to transform it into espresso coffee.
The continuous dispensing coffee machines have two water circuits: the first supplies fresh water to produce the espresso, while the second warms the heat exchanger from outside and supplies hot water and steam.
Bar and home espresso machines
Bar espresso machines function along the same principles as those designed for home use, so the component parts are also similar. The greatest difference is in the size: the larger size of the bar espresso machine, means that it is easier to keep the water temperature more stable, because the the boiler in which it is contained is larger. Consequently, the steam for foaming the milk is also always available. Behind the counter, we find machines with many metal parts, which guarantee the weight necessary to generate the best pressure conditions for the extraction of the coffee.
The components of the espresso machine
We have seen how espresso coffee is extracted in a continuous dispensing machine. Now let’s see what components the machine consists of and what functions they have.
- The water softener is installed in the space between the water network input and the espresso machine. It filters the water and reduces the hardness, since excessive limescale can have a negative effect on the resulting drink.
- The boiler contains hot water and steam. Inside, the cold water coming directly from the mains supply is heated thanks to a heat source, which may be an internal heating element, for electric machines, or an external burner for gas operated machines.
- The heat exchanger allows the water to reach the optimum temperature for making a good espresso quickly which is 90 °C. It is immersed in the boiler and is heated externally using hot water and the steam itself.
- The dispenser head is the component that the portafilter is attached to. This is kept thermally balanced via a system of thermosiphonic recirculation of the water: it is important to avoid drops in the temperature in the system that produces the espresso. A cold dispenser head could damage the quality of the drink.
- The pump, which is electrically operated, is needed to push the pressure up to 8-9 atmospheres, which is the pressure necessary to force the water through the block of ground coffee and extract the best substances from it. In fact the normal water pressure of the main water network is not enough to do this as it arrives at a pressure of around 1-3 atmospheres.
- The taps allow the steam to be used to foam the milk and heat liquids.
- The guages indicate the pressure of the water dispensed and the pressure in the boiler.
- The pressure switches are the instruments which control the pressure. They are positioned inside the machine and keep the water temperature in the boiler constant by inserting or withdrawing heating sources. The new generation of machines have electronic temperature probes, which carry out the same function.
- The solenoid valves regulate the correct flow of water or steam.
- The level regulator keeps the water level inside the boiler constant.
- The portafilters consist of a metal container inside which a filter is inserted, which can hold a dose of ground coffee enough to make one or two shots of espresso. They have a heat resistant handle and one or two spouts where the extracted coffee comes out.
- The shower filters distribute the hot water uniformly, forced by the pressure through the compacted block of ground coffee, and consist of a circular steel retina.
- The gasket of an espresso machine is made of silicon rubber and creates an air-tight seal between the dispenser head and the portafilter.
In order to ensure that your espresso machine works correctly, it is important to carry out maintenance activities regularly and frequently clean the steaming wand, the portafilter and also the grinder-doser: in this way, you can be sure to obtain and serve a top quality espresso.
Were you familiar with the functions of all the components of the bar coffee machine ?