- In 1909, Luigi Giarlotto’s machine showcased the first-known heat exchanger.
- In 1950, Beniamino Rota’s Condor machine brought baristas closer to controlling the pressure, and therefore the temperature, of the water in a heat exchange machine. Rota was the first to patent an espresso machine that featured an electric pump.
- A thermostat was used to regulate the temperature on the earliest espresso machines. It contained a wax pellet that melted within a sealed chamber and expanded at a set temperature. This in turn cracked open a spring-loaded valve to release the pressure.
- The heat source for the first espresso machines was gas or wood. A barista had to manually shut off, or at least turn down, the heat once the thermostat reached its set point temperature.
- Baristas do not typically use water from the steam boiler for brewing.
- As steam leaves the boiler, dissolved minerals that had been attached to the water molecules remain in the boiler. This limescale or other dissolved substance is capable of buffering away coffee flavour.
- By cycling hot water through the group, a thermosyphon helps keep the espresso machine’s brew temperature stable. It does so by harnessing the power of convection — not by use of a pump.
- The group head loses heat to the outside air, and the water inside it cools down. Because it is more dense, the cooler water sinks, passes through the lower pipe, and returns to the bottom of the heat exchanger.
- In 1955, Giampietro Saccani designed the first thermosyphon machine.
- In 1959, Faema launched the TRR, a pump machine equipped with two boilers. One boiler produced steam and the second produced hot water. The company had released a dual-boiler lever machine a few years earlier on a model called the President with Velox groups.
Offset temperature The difference between the water temperature in the boiler and the temperature of the water exiting the group head.