Does anyone know how upper-end espresso machines--the kind with the piston (pump handle)--work? What does the piston do? What is the principle of the espresso machine? How does one of those fancier espresso machines differ from my stovetop Mocha Express, which forces the water up through the grounds (via some sort of siphon principle)into the upper chamber?
Tnx in advance to any and all with good info.