 A gasket ensures a tightly closed unit and allows for pressure to safely build up in the lower section, where a safety valve provides a necessary release in case this pressure should get too high (with clean filters, that should not happen).The steam eventually reaches a high enough pressure to gradually force the surrounding boiling water up the funnel through the coffee powder and into the upper chamber (C), where the coffee is collected.Although the "boiler" on a moka pot contains "steam" at elevated temperature and pressure, the water forced up through the grounds is no hotter than that used in other brewing methods – up to 90 °C, depending on the stage of extraction.