Rather than pouring water over the coffee, water comes up through the bottom of the bed as it heats up and begins boiling. So, it’s almost like a pour-under coffee.
To use a Moka Pot, fill the bottom chamber with water. I recommend using water that’s just off the boil so it’s already hot, but if you want to start with room temperature or cold water that’s OK too. Fill the basket with finely ground coffee, shake gently to settle it, and place it in the bottom chamber (remember to handle carefully if you’ve filled it with hot water). Screw the top chamber on. Place it on your stove over medium-high heat. The steam generated from the heating water serves to “bloom” the water, evenly saturating the coffee bed and releasing the gases accumulating inside.
When the water in the bottom chamber approaches a boil, the pressure it generates will push it through the coffee bed, causing the coffee to extract. It should travel slowly up through the inner spout into the upper chamber. If it explodes out of the spout, your water is too hot. Conversely, if it bubbles and spurts inconsistently, turn the heat up. You’ll know it’s done when you hear a hissing sound, indicating there is no more water in the bottom chamber.
Moka pots are designed to be used on all stoves, but work best on gas stoves, or induction tops where you can manage and manipulate the heat easily. The ability to change the amount of heat with an open flame helps you finesse the temperature to hit that sweet spot. Gas stoves can sometimes supercede the temperature you want to heat the water to, but it’s not impossible to find that perfect temperature.
You can use any kind of coffee you’d like in a moka pot, but no matter what you choose, make sure you grind it finely, like espresso. The tighter you can pack the coffee, the more evenly the water will be able to pass through it and extract evenly as well.
I would recommend staying away from a lightly roasted coffee for this brewing method, because lighter roasted coffees tend to have more pronounced acidity. The uneven nature of the water passing through the coffee bed in a Moka Pot makes it more prone to uneven extraction no matter how well you control the variables. Uneven extraction tends to highlight that acidity even more than normal, which may leave you with a coffee that’s too bright for your preference.