Editing Espresso machine (section)

==Drive mechanism==
[[File:Morning Espresso Routine - Progress, Results, Observations and Miscellany.webm|thumb|Espresso being brewed (video)]]
Numerous 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.

===Piston-driven===
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[[File:Manual Elektra espresso machine.jpg|thumb|upright|A manual piston espresso machine made by Elektra]]

The piston-driven, 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 grounds. The act of producing a shot of espresso is colloquially termed ''pulling'' a shot, because these lever-driven espresso machines required pulling a long handle to produce a shot.<ref>{{cite book| last =Pendergrast | first =Mark | author-link= Mark Pendergrast | title =Uncommon Grounds: The History of Coffee and How It Transformed Our World | publisher =Texere | location=London |page=218|year=2001|orig-year=1999 | isbn =1-58799-088-1}}</ref> Lever-driven espresso machines are sometimes called manual espresso machines because of this.

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 (unit)|bar]]; 116 to 145 [[Pound per square inch|psi]]).

===Steam-driven===
[[File:Wigomat-espresso-kaffeemaschine.jpg|thumb|upright|A steam coffee machine]]
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.<ref name="timeline" >{{cite web
| url=http://www.cs.usyd.edu.au/~bob/Coffee/timeline.html
| title=An Espresso Timeline
| first=Bob
| last=Kummerfeld
| date=2011-03-14
| publisher=[[University of Sydney]]
| access-date=2018-07-30
| archive-date=2009-06-25
| archive-url=https://web.archive.org/web/20090625054808/http://www.cs.usyd.edu.au/~bob/Coffee/timeline.html
| url-status=dead
}}</ref> This design is still used today in lower-cost consumer machines, as it does not need to contain moving parts. Also, steam-driven machines do not produce as high a pressure for extraction compared with pump-driven. This results in the crema, a hallmark of an espresso, being of lower quality.

===Pump-driven===
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A refinement of the piston machine is the pump-driven machine, which was introduced in the [[Faema]] [[E-61|E61]] in 1961, and has become the most popular design in commercial [[Coffeehouse#Espresso bar|espresso bars]]. Instead of using manual force, a motor-driven pump provides the force necessary for espresso brewing. Espresso machines are made to accept water directly from a cold water line supply, common in commercial installations, or from a separate tank that must be filled with water by hand. The latter is more common with lower-volume commercial installations and domestic espresso machines. Due to the required high pumping pressure and precision flow control needed, the particular type of electric pumps typically used are known as ''solenoid-piston'' pumps. These pumps are classified as a positive displacement type (general category) of pump.

Four variants exist in home machines, depending on how brew water and steam are boiled; in discussion these are generally known by acronyms.
;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. However, they can perform only one operation at a time, requiring a warm up period between the execution of espresso pull and the milk frothing process. 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. Moreover, after the brewing process, a single boiler will expel (usually minor) quantities of water through the steam wand that were left over from brewing, which can cause the steam heated milk to then have a slightly watered down taste. To avoid this, the leftover water needs to be collected from the steam wand before steaming of the milk should begin. SB/DUs are generally found within the lower tiers of enthusiast home models, with steam wands being a simple and valued addition.
;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. Although the water for brewing remains at a lower range than that required for steaming milk, it is still too hot for proper coffee extraction without first cooling; thus this type of machine requires a cooling flush of 4–6 seconds prior to the first espresso pull. Once the machine is dialed into the proper temperature, as many shots can be pulled as required without refreshing. However, if the user leaves the machine idle again for some period, the flushing process will need to be repeated. The HX variety is found in many mid-range machines and many users install thermometers to assist them in dialing in correct temperatures. 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. One big advantage of heat exchanger over the other system is the water used for extraction is always fresh from the water source, which can be from the water tank or water network. The stale water gets flushed during the routine flushing. Instead of using stale stagnant water retained within the boiler.<ref>{{Cite web |last= |first= |date=2016-11-17 |title=Double Boiler Versus Heat Exchanger |url=https://www.finecoffeecompany.com/double-boiler-versus-heat-exchanger/ |access-date=2022-08-10 |website=Fine Coffee Company |publisher=Fine Coffee Company |language=en-US}}</ref>{{paragraph}} The first HX was the Faema E61 of 1961, a design nearly ubiquitous across the semi-automatic market segment of espresso machines.
;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. It is primarily found in higher-end machines, but also in some mid-range machines, overlapping with HX.{{paragraph}} 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,{{Citation needed|date=March 2011}} 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.{{paragraph}} In principle, TB machines yield a more stable brew temperature 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. The downside is the boiler specifically for brewing espresso consist of mainly stagnant water with little turnover, which repeatedly gets boiled again with little introduction of fresh water.{{paragraph}} The first DB was the [[La Marzocco]] GS of 1970.