Espresso began as a speed problem. In 1884 Angelo Moriondo of Turin patented a steam-driven device to serve coffee fast, but a closed boiler ties pressure to temperature, capping safe steam pressure at about one and a half to two bars. Luigi Bezzera’s single servings in 1901 and Desiderio Pavoni’s commercial La Pavoni machines after buying the patent in 1903 still produced strong, bitter, watery coffee with no crema. In 1945 cafe owner Achille Gaggia solved it with a lever that let a barista crush water through the coffee at nine bars, about 130 psi, emulsifying oils and carbon dioxide into crema and giving us the phrase pulling a shot.

Human arms tire, so in 1961 Faema introduced the E61 with a rotary positive displacement pump, and the fight moved to temperature. The episode explains single boilers, single boiler dual use machines, the heat exchanger’s copper tube that flash-heats fresh water through a steam boiler, and the dual boiler introduced in the 1970 La Marzocco GS, each with its own trade-off.

• A $30 home machine that only builds steam pressure is essentially 1903 technology.
• Heat exchanger machines need a cooling flush after sitting idle, or the brew water hits boiler temperature and scorches the coffee.
• Dual boiler brew water can sit for days in a quiet home or restaurant, which purists say flattens flavor.
• The E61 group head is a solid brass block weighing over nine pounds that acts as a thermal sink.
• Bottomless portafilters let baristas see channeling, when pressurized water drills through a weak spot in the puck.