Espresso Machines are used to make espresso.
Invented in 1901, multiple machine designs have been created to produce espresso. Several machines share some common elements.
Varying the fineness of the grind, the amount of pressure used to tamp the grinds, or the pressure itself can be used to vary the taste of the espresso. Some baristas pull espresso shots directly into a pre-heated demitasse cup or shot glass, to maintain a higher temperature of the espresso.
A steam-driven unit operates by forcing water through the coffee by using steam or steam pressure. The first espresso machines were steam types, produced when a common boiler was piped to four group heads so that multiple types of coffee could be made at the same time. The design is still used today in low-cost consumer machines, as it does not need to contain moving parts. Many low-cost steam-driven units are sold in combination with a drip-coffee machine.
The piston, or lever, driven machine was developed in Italy in 1945 by Achille Gaggia, founder of espresso machine manufacturer Gaggia. The design generically uses a lever, pumped by the operator, to pressurize hot water and send it through the coffee grinds. The act of producing a shot of espresso is colloquially termed pulling a shot, because these lever-style espresso machines required pulling a long handle to produce a shot.
There are two types of lever machines; manual piston and spring piston design. With the manual piston, the operator directly pushes the water through the grounds. In the spring piston design, the operator works to tension a spring, which then delivers the pressure for the espresso (usually 8 to 10 bar).
A refinement of the piston machine is the pump-driven machine, which was introduced in the Faema E61 in 1961, and has become the most popular design in commercial espresso bars. Instead of using manual force, a motor-driven pump provides the force necessary for espresso brewing. Commercial or some high-end home machines are often attached directly to the plumbing of the site; lower-end home machines have built-in water reservoirs.
Four variants exist in home machines, depending on how brew water and steam are boiled:
- Single Boiler (SB)
These machines can brew only, and not steam, requiring only a single boiler. They are relatively uncommon, with steam wands being a simple and valued addition.
- Single Boiler, Dual Use (SB/DU)
Some home pump espresso machines use a single chamber both to heat water to brewing temperature and to boil water for steaming milk. Since the temperature for brewing is less than the temperature for creating steam the machine requires time to make the transition from one mode to the other.
- Heat Exchanger (HX)
Some machines use a single boiler kept at steaming temperature, but water for brewing is passed through a heat exchanger, taking some heat from the steam without rising to the same temperature. This is found in many mid-range machines. There is some controversy as to the temperature stability of the brewing water, since it is indirectly converted from steaming temperature to brewing temperature, rather than kept at a brewing temperature. The first HX was the Faema E61 of 1961.
- Dual Boiler (DB)
Finally, in some espresso machines for commercial or home use, water for brewing is heated in a separate chamber, which requires two separate boilers. This is found primarily in higher-end machines, though it is also found in some mid-range machines, overlapping with HX.
The term "Dual Boiler" is used narrowly for machines with two separate boilers, and more broadly for what are more properly called Dual Heater (DH) machines, featuring a boiler for brewing and a separate thermoblock (TB) for heating brew water to steaming temperature – opposite to HX machines, where the boiler is at steaming temperature and is cooled to brewing temperature.
In principle, TB machines yield stabler brew temperatures at the expense of steaming performance and speed, while HX machines yield better steaming at the expense of stable brew temperature. True DB machines provide stable brew temperatures and fast steaming, but are larger and more expensive.
In recent years air-pump driven espresso machines have emerged. These machines use compressed air to force the hot water through the coffee grounds. The hot water is typically added from a kettle or a thermo flask. The compressed air comes from either a hand-pump, N20 or CO2 cartridges or an electric compressor. One of the advantages of the air-pump driven machines is that they are much smaller and lighter than electric machines. They are often handheld and portable. The first air-pump driven machine was Handpresso Wild, which was invented by Nielsen Innovation SARL, a French innovation house, and introduced in 2007.