The moka pot is a stove-top or electric coffee maker that produces coffee by passing boiling water pressurized by steam through ground coffee. It was patented for the first time in Italy by the inventor Luigi De Ponti for Alfonso Bialetti, in 1933. Bialetti Industrie continues to produce the same model under the name "Moka Express".
The moka pot is most commonly used in Europe and in Latin America. It has become an iconic design, displayed in modern industrial art and design museums such as the Wolfsonian-FIU, Museum of Modern Art, the Cooper–Hewitt, National Design Museum, the Design Museum, and the London Science Museum. Moka pots come in different sizes, from one to eighteen 50 ml cups. The original design and many current models are made from aluminium with bakelite handles.
Variations and brands
Traditionally, moka pots are made of aluminium and are used over a flame or electric range. The aluminium moka pots cannot be used on induction stoves. There are, however, also many stainless steel models available. Electric self-heating moka pots are also available, as well as induction specific moka pots made of a titanium-alloy base.
"Brikka" is a modified moka pot manufactured by Bialetti. It incorporates a weighted valve as a pressure regulator on top of the nozzle that allows pressure to build up inside the water tank in a manner similar to a pressure cooker. As pressure builds up more quickly in this method (since there is much less leakage of vapour) compared to the standard moka pot, it reaches the level required for water to rise through the ground coffee in a shorter time. However, the weighted valve allows pressure to accumulate and temperature to rise somewhat further before the liquid bursts through the nozzle. The result is coffee brewed at a higher pressure and temperature than the standard pot, making it more similar to espresso, and therefore with more visible crema.
"Mukka Express" is a modified moka pot also manufactured by Bialetti that allows milk to be frothed and mixed with the coffee during brewing. The name, "Mukka", is a pun on the Italian for milk-cow, mucca. Bialetti also manufactures several stainless steel moka pots, e.g.: Musa, Class and Venus.
Also the high quality and design oriented Italian kitchenware manufacturer Serafino Zani is known for his moka pots: "Finlandia" designed by Tapio Wirkkala, "Mach" designed by Isao Hosoe and awarded with the Good Design Award (Chicago) 1993, "Thema" in stainess steel with titanium and "Genesis" in stainless steel and copper, both designed by Tarcisio Zani.
Vev Viganò is an Italian manufacturer that specialises in stainless steel moka pots. Their product lines include Kontessa, Itaca, Vespress and Carioca.
Top Moka, another Italian manufacturer, offers two different styles of moka pots in a wide variety of colours. The more traditional Top Moka pot comes in sizes varying from two- to six-shot boilers. They also make mini moka pots in one- and two-shot sizes that use dispensing arcs rather than the standard collection chamber. Both are available with aluminium boilers for standard cooktops or titanium-alloy boilers for induction stoves.
Brewing coffee with a moka pot
The boiler (marked A in the diagram) is filled with water almost up to the safety release valve and the funnel-shaped metal filter (B) is inserted. Finely-ground coffee is added to the filter as shown below. Then the upper part (C, which has a second metal filter at the bottom) is tightly screwed onto the base. The pot is placed on a suitable heat source, the water is brought to its boiling point, and thereby steam is created in the boiler.
A gasket ensures a tightly closed unit and allows for pressure to safely build up in the lower section, where a safety valve provides a necessary release in case this pressure should get too high (with clean filters, that should not happen).
The steam eventually reaches a high enough pressure to gradually force the surrounding boiling water up the funnel through the coffee powder and into the upper chamber (C), where the coffee is collected. Although the "boiler" on a Moka pot contains steam at elevated temperature and pressure, the water forced up through the grounds is no hotter than that used in other brewing methods - up to 90C, depending on the stage of extraction.
When the lower chamber is almost empty, bubbles of steam mix with the upstreaming water, producing a characteristic gurgling noise. This "strombolian phase" allows a mixture of superheated steam and water to pass through the coffee, which leads to undesirable results, and therefore brewing is stopped as soon as this stage is reached.
Moka pots require periodic replacement of the rubber seal and the filters, and a check that the safety release valve is not blocked.
After use, a thin coat of oily coffee residue is left lining the interior of the stems, filters and upper chamber. It is said to be desirable to retain this residue, as it subsequently prevents coffee from acquiring an unpleasant metallic taste through contact with the aluminium wall. However if a moka pot is left unused for long periods of time this oily film of vegetable fats would go rancid and contaminate the taste of coffee as soon as the pot is put into use again. To avoid this a long-unused moka pot should be cleaned by filling its tank with a measure of water and soap and allowing the soapy water to flow through the funnel, filter and stem cleaning them from the rancid fat. It may then be helpful to recreate a fresh oil 'skin' with a throw-away coffee brew. 
Moka pot dimensions
The Moka pot comes in various sizes based on the number of 50 mL espresso cups they produce. The following table are the standard sizes for the Bialetti Moka Express.
|Metric units||US units|
|1||60 mL||133 mm||64 mm||2.0 fl oz||5¼"||2½"|
|3||200 mL||159 mm||83 mm||6.5 fl oz||6¼"||3¼"|
|6||300 mL||216 mm||102 mm||10.0 fl oz||8½"||4"|
|9||550 mL||254 mm||105 mm||18.5 fl oz||10"||4⅛"|
|12||775 mL||292 mm||127 mm||25.0 fl oz||11½"||5"|
Moka coffee characteristics
The flavour of Moka pot coffee depends greatly on bean variety, roast level, fineness of grind, water profile, and the level of heat used.
Moka pots are sometimes referred to as stove-top espresso makers and produce coffee with an extraction ratio similar to (but somewhat higher than) that of a conventional espresso machine. The resultant brew has increased extraction of caffeine and flavours from the grounds versus filter coffee, resulting in a stronger brew than that obtained by drip brewing. Furthermore, depending on bean variety and grind selection, Moka pots can create a foam emulsion, known as crema.
However a typical Moka coffee is extracted at relatively low pressures of 1 to 2 bar, while standards for espresso coffee specify a pressure of 9 bar. Therefore Moka coffee is not considered to be a true espresso and has different flavour characteristics.
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Media related to Moka Expresses at Wikimedia Commons