A dynamic preheater assembly ensures that water entering the coffee boiler is precisely 170 degrees F. 170 degree F water replaces hot water exiting the group, reducing temperature swings in the coffee boiler. An algorithm-based PID temperature controller further reduces temperature fluctuation in the coffee boiler. A group cap designed by Piero Bambi and an integrated ruby flow restrictor reduces channeling and ensures that water never leaves the saturated area of the coffee boiler; this eliminates the introduction of temperature instability during the brewing process.