Why roast level changes the right temperature
Darker roasts have more soluble compounds sitting close to the bean surface, broken down by longer roasting times. Pour water that's too hot over a dark roast and you pull those compounds out fast, producing the bitter, ashy cup people associate with "burnt" coffee. Light roasts are the opposite problem: their density and under-developed sugars resist extraction, so water that's too cool leaves the cup sour and thin.
What we tested
We brewed the same Ethiopian light roast, a Colombian medium roast, and a Sumatran dark roast at five temperatures each, from 88 °C to 96 °C, using a Precision Gooseneck Kettle set in 1 °C steps to remove temperature drift as a variable. Each cup was scored blind by three tasters on the SCA cupping scale.
Light roasts scored highest at 94–96 °C. The higher energy was needed to break down the denser cell structure and pull out enough sugar to balance the acidity. Below 92 °C, every light roast cup scored as sour and thin.
The numbers that worked
Medium roasts peaked at 92–94 °C, a wide enough window that most pour-over guides default here. Dark roasts scored best at 88–90 °C: anything above 91 °C consistently pulled out bitterness that masked the chocolate and caramel notes tasters were looking for.
If you only remember one number: start at 93 °C for an unknown roast, then adjust down 2–3 °C if it tastes bitter, or up 2–3 °C if it tastes sour. That's the full range we found worth testing.
