This is an excellent write-up on the many different types of Espresso Machines by KK Yoon.
If you still have not visited the forum, now is the time.
Cold water is pumped through a serpentine path inside a thermoblock ( heated metal block ) to brew espresso. To produce steam, the thermoblock is heated to a high temperature and the pump is then turned on in pulses. Each pulse feeds a small amount of water into the thermoblock – the water immediately boils into steam.
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