Espresso Machine
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An espresso machine is used to produce the traditionally Italian coffee beverage called espresso. A professional operator of such a machine is called a barista. The knowledge required in making the finest espresso is considered to be a craft, similar to artisan baking.

The act of producing a shot of espresso is colloquially termed "pulling" a shot, deriving from lever-style espresso machines that required pulling a long handle to produce a shot. To pull a shot of espresso, a metal filter-basket is filled with either 7-10 grams or 12-18 grams of ground coffee for a single shot (30mL) or double shot (60mL), respectively. The espresso is then tamped, or compressed with approximately 30 lbf (130 N) of force into a densely packed puck of espresso. The portafilter (or group handle) holds the filter-basket and is locked under the grouphead's diffusion block. When the brew process begins, pressurized water at 90±5°C (200±9°F) and approximately 900 kPa (130 PSI, or 9 bars) is forced into the grouphead and through the ground coffee in the portafilter. Water cooler than the ideal zone causes sourness; hotter than the ideal zone causes bitterness. High-quality espresso machines control the temperature of the brew water within a few degrees of the ideal.

This process produces a rich, almost syrupy beverage by extracting and emulsifying the oils in the ground coffee. An ideal double shot of espresso should take 20-25 seconds to arrive, timed from when the machine's pump is first turned on. Varying the fineness of the grind, the amount of pressure used to tamp the grinds, or the pump pressure itself can be used to bring the extraction time into this ideal zone. Most prefer to pull espresso shots directly right into a pre-heated demitasse or shot glass, to maintain the ideal temperature of the espresso.

An espresso machine also has a steam wand which is used to steam and froth milk for milk based espresso beverages such as the cappuccino and latte.

A recent North American brewing trend came with the invention of the bottomless portafilter, that is, a portafilter without the bottom half, exposing the basket and causing the espresso to not contact metal during the extraction process. The bottomless portafilter serves as a tool to analyze evenness of grind distribution and tamping, as more volume of espresso will flow from low-density areas of the coffee puck. Some claim to prefer the taste, citing the portafilter preserves crema.

Types of Espresso Machines

Stovetop Espresso Maker

Commonly found in Italy, stovetop espresso makers produces a dark coffee with an extraction ratio similar to that of a conventional espresso machine. The bottom chamber contains the water. The middle chamber is a filterbasket and sits within the bottom chamber holding the ground coffee. The top chamber, with a metal filter, screws onto the bottom chamber. When the pot is heated on a stove, the pressure from the steam in the bottom chamber forces the water through a tube into the filter-basket, through the ground coffee, the metal filter, and it then funnels into the top chamber where the coffee is then ready to serve. They should be disassembled after use, cleaned and dried before reuse.

Stovetop espresso makers are conveniently portable, since they require no electricity to use. This makes them great for tourists and hikers. Stovetop espresso makers produce dark coffee, but they usually lack the necessary pressure which creates a foam emulsion known as crema.

Stovetop espresso makers are known colloquially as moka pots, after an early trademark. They are also known as a macchinetta or little machine. Sometimes they are referred to as Spain coffee makers.

Steam Espresso Maker

Similar to a stovetop espresso maker, a steam unit operates solely by steam pressure, but is fashioned more in the style of a typical pump-powered unit, including the filter-holding/coffee dispensing head called a portafilter. Steam units generally produce a product more or less identical to a stovetop espresso pot.

Piston-Driven Espresso Maker

Now mostly characteristic of the showpiece high-end designs of La Pavoni, the piston-driven espresso maker is the archetype of the modern espresso machine, and the origin of the crema, which was originally thought to be an undesirable waste product but is now considered characteristic of a properly made shot of espresso. It was invented in 1938 by Achille Gaggia; while it is still considered a good way to make espresso, it requires some strength to operate, and most such units sold today are as much showpieces as practical devices.

Traditional Pump-Driven Espresso Machine

A refinement of the piston machine is the pump-driven machine, which has become the most popular design in commercial espresso bars. Instead of using manual force, a motor-driven pump provides the force nessary 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.

Semi Automatic Espresso Machine

Semi-automatic espresso machines are automatic in the sense water is delivered by a pump, rather than manual force and remaining brew pressure in the basket is dissipated with a three way valve. Coffee grinding, dosing and tamping is prepared manually, and brew volume is controlled manually, resulting in the term semi-automatic.

Automatic Espresso Machine

Automatic espresso machines are similar to semi-automatic except have a flowmeter installed inline with the grouphead. When the programmed amount of water has flowed through the flowmeter, the pump is automatically turned off and brew pressure released through a three way solenoid valve.

Super Automatic Espresso Machine

These machines operate by automatically grinding the coffee, tamping it, and extracting in much the same way an automatic espresso machine does. The difference is they are fully self-contained; all you do is fill the bean hopper and water reservoir. After brewing, the machine will automatically dispose of the spent puck into a collection container. Many of these machines have coffee dosing, water flow, and shot temperature adjustability. Additionally, many models now feature automated milk frothing devices. These models are becoming increasingly popular for home use, but due to the automated nature usually result in lower quality coffee than that produced by a skilled operator using an automatic or semi-automatic machine. Two popular manufacturers of such machines are Jura-Capresso and Saeco.

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