A moka pot brews with steam pressure.
Water heated in the base builds pressure and rises through the coffee. Starting with hot water and medium heat keeps the coffee from cooking and turning bitter.
What it is
A stovetop pot in three parts: water goes in the base, ground coffee in the funnel, and the brewed coffee rises into the top chamber. As the water heats, steam pressure pushes it up through the coffee.
Why it matters
The moka's enemy is too much heat for too long: the coffee cooks, and the cup turns harsh and burnt. Starting with water that's already hot shortens the time on the stove, and medium heat keeps the flow gentle.
In practice
Fill the base with hot water to just below the valve. Fill the funnel with fine coffee, level it without pressing, and screw the pot closed (use a cloth — it's hot). Medium heat, lid open so you can watch. Let it flow in a steady stream; when it turns pale and starts to hiss, take it off the heat and cool the base under cold water to stop the brew.