If you’ve ever used a percolator, then you understand the rudiments of how a moka pot works. It’s pretty simple, although not as basic as a French press, Chemex or AeroPress. With a moka pot, water is added to the bottom chamber, and then the pot is placed over a heat source (a gas or electric stove eye, usually, but there are self-heating units on the market).
Once the water begins to approach boiling temperature, steam power forces it up the central tube and into the basket holding the coffee grounds. The force of the steam continues to move the water (now coffee) upward through the upper tube, where it collects in the top chamber. Once the brewing process is finished, you simply pour a cup of coffee through the spout.
There are a few differences between a moka pot and a regular percolator. The first and one of the most important differences is the chambered design. A regular percolator uses just one large chamber, with a basket to hold ground coffee attached to a long tube that sits on a base in the carafe.
Another difference is that moka pots are pressurized. They use a rubber gasket to prevent steam and heat from escaping, allowing them to build to boiling temperature much more quickly than a percolator, which often lacks pressurization. Finally, there’s a pressure relief valve built in that allows excess pressure and heat to escape without letting it all out.