I don't know what machines Starbucks outlets are using. I have never done part-time jobs at fast food restaurants, unlike
@sbfuncle. I'm not very smart, so I couldn't handle work and studies at the same time.
The big semi-auto commercial machines they are either dual boilers or single boiler with heat exchanger. Dual boilers are simple - one for brewing one for steaming. Steaming requires a higher temperature, as you know. You should not use steaming temperature to brew coffee.
Heat exchanger is a single boiler with with a pipe (rod) running through the middle of the boiler. The water that passes through the pipe is the one that is being used to brew the coffee, and as it passes through it receives heat from the "surrounding" boiler via thermodynamics and hydrodynamics. You can understand single boiler to mean a boiler within a boiler.
Of course, dual boilers are more expensive because there are 2 boilers, and more premium.
Like that KYM ?