How a Stove-top Espresso Maker Works
The science behind espresso making is concerned with applying a greater amount of pressure, or force on the coffee grounds then normal gravity, in order to extract more of the coffee's flavour. For an espresso, by definition of the term, the coffee grounds need to be subjected to between 7-9 bar of pressure.
Although stove-top espresso makers operate under a much lower pressure, typically 1 bar, they still generate enough pressure to make great-tasting espresso style coffee.
1. When you prepare your stove-top espresso maker for use, air gets trapped inside the water tank.
2. When heat is applied to the stove-top espresso maker, the air and water inside expand. As they are contained within the water tank, this leads to a build up of pressure in the tank.
3. Eventually, the pressure builds up to the point where the hot water is forced up through the coffee in the filter basket into the upper chamber of the stove-top espresso maker.