- Modern espresso machine boilers are quite basic and usually manufactured from brass, copper, or stainless steel.
- Copper is extremely thermally conductive; brass is easy to machine a very thermally conductive; whilst stainless steel has very different properties.
- Stainless steel is hard and unlikely to dent, but that makes it more difficult to machine. But it has the benefit of being 100% lead free whereas brass usually contains a very small amount of lead.
- Even machines with stainless steel boilers often have many brass components. Fortunately, studies show that lead contamination in coffee is extremely low and below levels considered to be harmful to the health of adults. However, water samples taken immediately after a brass boiler is descaled show much higher levels of lead for a short period.
- Tubular heating elements are used in most espresso machine boilers. The tubes are usually copper or stainless steel.
- To generate heat, the electricity is channelled through the inside of the heating element via a wire that works as a metal conductor. The conductor is usually made from nickel and chromium [aka Nichrome].
- Heating elements are filled with nonconductive compact powder for insulation, to prevent electric current from escaping.
- Espresso machine steam boilers are fitted with safety valves to allow steam pressure escape in the unlikely event of a machine’s pressurestat malfunctioning.
- Boilers are also fitted with an anti vacuum (antivac) valve to allow air into the boiler after it is switched off. This prevents a vacuum from forming inside the boiler.
- The first known machine designed with a single-serve portafilter was the Luigi Bezzera machine from 1901.
- The first patent for a double spouted portafilter was filed in 1918 by Pier Teresio Arduino.
- In 1939, the first known design for a horizontal espresso machine was drawn up by Guiseppe Bambi, co-founder of La Marzocco.