The single-circuit machine is the simplest version of espresso technology. The system consists of a single boiler, correspondingly, there are few pipes and parts inside such a machine. Our model shows a version with a vertical boiler, which is the most common design. As already mentioned with dual-circuit machines, the main problem in the design of an espresso machine is the difference between the optimal temperature for coffee and steam extraction. While this is solved through the use of technology in dual-circuit and dual-boiler machines, in a single-circuit machine, the barista is left to manually switch between two different temperature levels.
In the normal state, the coffee setting, the boiler is completely filled with water. The machine's temperature control is set so that the temperature at the brewing group is around 92°C. With this setting, an espresso can be made using the usual procedure. If you then want to froth milk, a boiler temperature of around 105°C and a pressure of around 0.2-0.3 bar is not really enough. To generate a reasonable amount of steam, two parameters must be changed. First, the boiler temperature must be increased so that the pressure rises to 1 bar, and space must be made for the resulting steam. In practice, you switch to steam mode and open the steam tap at the same time. At first only water comes out of the nozzle, after a few seconds almost exclusively steam, then you close the steam tap. Now there is enough space in the boiler for a sufficient steam volume.
After frothing, the machine needs to be brought back into the correct state for the next espresso. Single-circuit machines have a switch that operates the pump. You switch back to espresso mode, open the steam tap, and turn on the pump. After a few seconds of steam, only water comes out of the nozzle. The steam tap can be closed and the pump turned off again. The machine now needs a moment to stabilize the temperature, then it is ready for the next espresso.
Single-circuit machines are usually more affordable due to their simple technology and straightforward components, but they are not recommended for every requirement. For example, in a household where drinks primarily contain milk, frequent switching is quite inconvenient. It's also important to remember that the machine is thrown off course each time it's used and then needs some time to reach a stable brewing temperature. A single-circuit machine is primarily a pure espresso machine with the option of occasionally frothing.
