Roast level changes how easily a bean gives up its solubles, and temperature is one of the levers that compensates.
The numbers
Light roast — 94 to 96 °C (201 to 205 °F), and boiling water is defensible for very light Nordic profiles.
Medium — 92 to 94 °C (198 to 201 °F).
Dark — 88 to 92 °C (190 to 198 °F).
Why light roasts want more heat
Roasting breaks down the bean’s cell structure. The less roasting, the more intact and dense the bean, and the more resistance the water meets.
A light roast at 88 °C (190 °F) will taste sour no matter how fine you grind.
Why dark roasts want less
Dark roasts are porous and brittle, and they extract easily. Hot water pulls the bitter compounds too readily, and the result is ashy.
The alternatives to temperature
Temperature is one of three levers, and the others often work as well:
Grind finer — more surface area. Extend contact time.
If your kettle has no temperature control, grinding is the equivalent adjustment.
Espresso
Same logic, and machines vary in how much control they offer. A PID makes it a setting; a basic thermostat makes it a guess.
Light-roast espresso is where temperature control earns its money.
The measurement caveat
What the kettle reads is not what the coffee gets. Heat is lost to the dripper, the filter and the carafe.
Preheat everything, or accept that you are brewing several degrees cooler than you think.
What people want to know
What if my kettle has no temperature control?
For light roasts, pour straight off the boil. For dark roasts, wait about a minute after boiling, or add a splash of cold water to the kettle; then fine-tune with grind size rather than temperature.
Last reviewed 30 October 2026