Moka pots are similar to espresso machines in that they brew under pressure, produce coffee with an extraction ratio similar to that of a conventional espresso machine, and, depending on bean variety and grind selection, Moka pots can create the same foam emulsion known as crema that conventional espresso machines can.
Moka pots differ from espresso machines in that they brew under substantially lower pressure – 1.5 bars rather than 9 bars – and use hotter water – a mix of boiling water and steam at above 100°C (rather than 92°–96° of espresso machines), similar to early steam brewing machines.
Moka pots are widely agreed to produce inferior quality brewing to espresso machines, due to brewing at excess heat and insufficient pressure, but are considerably cheaper and more convenient than espresso machines, and the quality of brew is prized and preferred by many over unpressurized brewing.
The bottom chamber contains the water. The middle chamber is a filter-basket 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 are commonly found in Italy, Spain and Portugal.
They are known as a macchinetta, Italian for "little machine".