Pretty good article. Worth to read

Source: http://www.konacoffeeroasting.com/anatomy-of-an-espresso-machine/

by dan

The first thing any aspiring barista will become familiar with on an espresso machine is the portafilter, which is also called the filterholder or groupo. The portafilter holds the filter basket which in turn holds the roasted, ground, tamped coffee as the espresso is brewed.

The portafilter may have either one or two spouts that allow the espresso to pour out during brewing. Most portafilters are made from either chrome-coated brass, aluminum, copper, or steel, and with a heat-resistant handle.

The filter basket is a bowl-shaped, perforated metal basket that inserts into the portafilter and holds the ground coffee. Holes in the filter basket allow brewed espresso to seep through and flow out the spout into the waiting demitasse. The filter basket may be a single or double basket to produce either a single or double shot of espresso. Convertible baskets will produce either.

The barista grabs the handle of the portafilter in order to clamp or unclamp it from the group, which typically protrudes from the front of the espresso machine. The group is also known as the brewhead or delivery group.

The brew group includes the portafilter, filter baskets, and grouphead, and may be passively or actively heated by contact with the boiler. The grouphead includes the portafilter locking connector and dispersion screen.

As a part of the brew group, the dispersion screen ensures the proper dispensing of water evenly and in a wide pattern over the bed of roasted and ground coffee with the goal of simultaneously saturating all of the coffee in the portafilter/filter basket.

The boiler is the espresso machine’s heat-producing unit and is usually made from steel, brass, copper, or aluminum.

The drip tray is beneath the cup tray which holds the demitasse during brewing. The drip tray and cup tray are beneath the brew group.

An espresso machine’s cup warmer area is typically on the top of the machine directly above the boiler. Though not all espresso machines have cup warmers, some have actively heated cup warmers.

Most home espresso machines have a reservoir that holds the water used to brew the espresso and also to supply the steam that emits from the steam wand and is used to froth milk for specialty espresso drinks such as cappuccinos, lattes, and mochas. The steam wand, also called the nozzle or stylus, may also be used to heat water or dispense hot water.

An espresso machine usually has a control panel that includes various controlling knobs or switches (either rocker type, pressure sensitive, or push-button) such as the power switch, brew control, steam control, and a switch allowing hot water to be dispensed.

The frothing knob controls the steam pressure that comes out of the steam wand, releasing steam from the espresso machine’s internal boiler, or thermoblock.

Most home espresso machines have a vibratory pump with a diaphragm that expands and contracts to create high pressure (e.g., 135 pounds per square inch) to brew espresso, while commercial machines often have a rotary pump that uses oscillating vanes to create high pressure.

Many espresso machines have a pressure relief system (three way valve system; three way solenoid) that automatically removes pressure from the portafilter after brewing espresso so that the portafilter may be quickly removed without a dangerous release of pressure (a portafilter sneeze).

More advanced espresso machines, including automatic espresso machines and super automatic espresso machines, feature a preinfusion option that pre-wets the bed of tamped coffee in the filter basket in the portafilter for a few moments before the brewing of the espresso shots commences. This is typically done by a pump that briefly activates, pauses, and then reactivates to complete the brewing.

The well-known E61 grouphead features a process known as progressive preinfusion that involves a pump activating to fill a secondary chamber before the espresso machine’s full pressure kicks in and is applied to the bed of coffee.

Progressive preinfusion, also known as natural preinfusion, results in three to seven seconds of saturation time previous to full pressure, and is considered by many to be the superior method of extracting the coffee’s best flavors and aromas into a concentrated, intense espresso shot.

An integral tool associated with the espresso machine is the coffee tamper, a small, pestle-like device which is flat on one end and held by the other end in order to compact ground coffee into the filter basket for espresso brewing. A standard tamper size is 58 mm (the internal diameter of the filter basket).

A review of the history of espresso machines is like taking a journey along the road toward a better espresso shot, a quest that continues to evolve today. It all began in 1822 when an espresso machine prototype was invented in France. The first commercial espresso machine didn’t come until 1905, this time in Italy.

Q. What’s the difference between the old PL041 and the new model ?

A. The only substantial changes are the steam wand and the OPV. The OPV on the new one is adjustable but Lelit recommends not to fiddle with it. Lelit just did the right thing and adjusted it down to 9bar in the new version which should help make already great shots even better. What they really needed to do was make a significant improvement to the steam wand. The new one is the same length (which is just a little bit short) as the previous one. Regardless, with practice and proper technique as described elsewhere on CG, it’ll steam with the best machines in the class.