Espresso: Machines

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[edit] ESPRESSO: MACHINES

An "Espresso Machine" is generally considered to be a device which contains a means to supply and force heated water through ground coffee placed into some form of perforated container. That force may equate to 4-18 BAR. The resultant flow is considered to be espresso. There are a few common ways to do this which are listed below somewhat in order of appearance upon a time line from the beginning of the 20th century. A common accessory is a portafilter, which is an easily removable device which holds a metal, bottom perforated, basket designed to contain ground coffee in a way to allow the heated water to flow through and into a container as espresso. Two terms defined:

• A kettle is an open heating container which operates below or at the temperature of the normal boiling point of water.
• A boiler is a closed heating container which operates below, at, or above the normal boiling point of water.

--Steam operated espresso machines--

• These machines consist of a boiler and ground coffee container. They have a means to control the flow of water, heated to steam temperature, from the boiler through ground coffee contained in a device such as a perforated basket placed into a portafilter.

--Lever operated espresso machines--

• Direct action lever operated machines have boiler or kettle supplied heated water. The brewing action is performed by direct operator pressure upon the lever causing movement through an arc. By mechanical action and valving this pressure causes the hot water supplied by the source to be pressed through the ground coffee previously placed in some device such as a portafilter.

• Spring lever operated machines have boiler or kettle supplied heated water. The brewing action is performed by operator pressure upon the lever causing movement through an arc which stores energy in a strong spring. This force, when the lever is released and through mechanical action and valving, causes the hot water supplied by the source to be pressed through the ground coffee previously placed in some device such as a portafilter.

--Pump operated espresso machines--

• Pump operated machines have boiler supplied heated water. The action is caused by the pump forcing water into a portion of the heated boiler which then is routed through the ground coffee previously placed in some device such as a portafilter.

• The Vibratory pump is operated by alternating electrical current from the mains in such a way as to allow magnetic fields to oscillate the internal piston and, through the internal valving, to move small amounts of water through it with great force. It is similar in action to a old style pitcher pump.

• Rotary pump operated machines have boiler supplied heated water.The action is caused by the electrically operated rotating vane pump forcing water into a portion of the heated boiler. This water is then is routed through the ground coffee previously placed in some device such as a portafilter.

--Variations--

• A machine may have any, none, or all of the following features.

• The group may be mounted directly to the bottom of the heated boiler or kettle.

• Thermosiphon ( Thermosylphon) A thermosiphon is a device which allows water from a boiler to be circulated through the group which is a permanent mechanical device designed to hold a loaded portafilter. The heated water is caused to move through the passages by thermal convection. This action causes the group and portafilter to achieve a temperature above the ambient. This in turn allows the brew water to retain much of its heat while being transferred to, and through, the ground coffee.

• Heat exchange (HX) A heat exchanger is a device contained within a boiler and or kettle which transfers thermal energy into another separate set of water passages by direct conduction of the internal heat to these passages being contained within the larger mass of fluid. It is a method of variably adjusting the heat of the brew water through liquid flow from the group prior to the dispensing of the beverage. This flow may also be used to pre-heat or cool the group to a temperature above room ambient. This is a common feature to allow the operator to control the temperature of the brew as the brews are being serially produced.

This TMC Wiki page is about types of espresso machine. It is currently a stub that requires the addition of further content.