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Moka pot
The moka pot[1][2] is a stove-top or electric coffee maker that brews coffee by passing hot water driven by vapor pressure and heat-driven gas expansion through ground coffee. Named after the Yemeni city of Mocha, it was invented by Italian engineer Luigi Di Ponti in 1933 [3][4][5] who sold the patent to Alfonso Bialetti, an aluminum vendor. It quickly became one of the staples of Italian culture. Bialetti Industries continues to produce the original model under the trade name "Moka Express". Spreading from Italy, the moka pot is today most commonly used in Europe and in Latin America. It has become an iconic design, displayed in modern industrial art and design museums including the Wolfsonian-FIU, the Cooper–Hewitt, National Design Museum, the Design Museum,[6] the London Science Museum, The Smithsonian and the Museum of Modern Art.[7] Moka pots come in different sizes, making from one to eighteen 50 ml (2 imp fl oz; 2 US fl oz) servings.[8] The original design and many current models are made from aluminium with Bakelite handles, though they are sometimes made out of stainless steel or other alloys. Some designs feature an upper half made of heat-resistant glass. Use  Moka pots are used over a flame or electric range. Stainless steel pots, but not aluminium, can be used with induction cooking. A number of physics papers were written between 2001 and 2009 utilizing the ideal gas and Darcy's laws, along with the temperature-dependent vapor pressure of water to explain the moka pot's brewing process.[9] A rubber gasket ensures a tight seal between components, and a safety valve prevents over-pressurization. PreparationThe boiler (marked A in the diagram) is filled with water to an etched line (or slightly below the safety release valve). While at-home makers generally do not preheat the water used, it can expedite the brewing process in commercial settings.[10] The metal filter funnel (B) is inserted. Finely ground coffee is added to the filter. How tightly the coffee is packed impacts how quickly the coffee extracts and the strength of the brew.[11] The collector (C) is then attached and the pot is heated, so that the water boils. BrewingThe heating of the boiler (A) leads to a gradual increase of the pressure due to both the expansion of the enclosed air and the raised vapor pressure of the increasingly heated water. When pressure becomes high enough to force the water up the funnel through the coffee grinds, coffee will begin to pour into the upper chamber (C). When the lower chamber is almost empty, bubbles of steam mix with the upstreaming water, producing a characteristic gurgling noise—a signal that brewing should be stopped. Navarini et al. call this the "strombolian" phase of brewing, which allows a mixture of highly heated steam and water to pass through the coffee, which leads to rapid overextraction and introduction of undesirable flavors.[11] Unlike a standard percolator, the moka pot never sends brewed coffee back through the coffee grounds.  Funnel with ground coffee  Mid-brew, showing brewed coffee in the process of being transported through the funnel  Layer of crema developing MaintenanceMoka pots require periodic replacement of the rubber seal, a scouring of its removable filter, and a check that the safety release valve is not blocked. All parts of the pot should be scrubbed by hand using a mild detergent, as aluminium moka pots are not dishwasher safe.[12][13][14] Aluminium migrationThe potential for toxic amounts of aluminium migration being created by brewing an acidic beverage in an aluminium pot have been scientifically investigated, and determined to be "negligible" – falling below 1% of recommended total weekly intake level once a new pot has been used.[15] Following the pot's stabilization at below 1% with regular use, migration rose to a maximum observed level of just under 4% after a dishwasher cleaning, resulting in dishwasher use being strongly discouraged. Pot sizesThe moka pot comes in various sizes based on the number of 50 ml (2 imp fl oz; 2 US fl oz) espresso cups they produce. The following table lists the standard sizes for the Bialetti Moka Express.
Moka coffee characteristicsBrewed coffee flavor, including that of a moka pot 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. However, a typical moka coffee is extracted at relatively low pressures of 1 to 2 bar (100 to 200 kPa),[11] while standards for espresso coffee specify a pressure of 9 bar (900 kPa). Therefore, moka coffee is not considered to be an espresso and has different flavor characteristics.[clarify][16][17] Variations and brands
  Among the variations to the moka pot design that have been introduced are those to expedite brew time, create milk froth, and allow microwave brewing. To expedite brewing, a weighted valve called Cremavent has been added 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. 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. [citation needed] Another variation allows for milk to be frothed and mixed with the coffee during brewing.[19] See alsoNotes
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