Light roasts need more heat than medium or dark, because they are physically harder to extract.
Why
Roasting breaks down the bean’s cell structure. The less roasting, the more intact and dense the structure, and the more resistance the water meets.
A light roast at 90 °C will taste sour no matter how fine you grind.
The numbers
Light roast — 94 to 96 °C. Some people brew very light Nordic roasts at a full boil, and it works. Medium — 92 to 94 °C. Dark — 88 to 92 °C. Dark roasts extract easily and turn bitter and ashy at high temperature.
The other levers
Temperature is not the only way to get there. Grinding finer and extending contact time do the same job.
Use whichever is available. A kettle without temperature control still lets you grind finer.
Espresso
The same logic. Light roast espresso is typically brewed at 94 to 96 °C, against 90 to 93 for a medium.
Machines without temperature control are at a real disadvantage with light roasts, which is one reason PID kits sell.
Measuring it
A kettle that reads 96 °C is not delivering 96 °C to the coffee. Heat is lost to the kettle spout, the dripper, the filter and the carafe.
Preheat everything — rinse the filter with hot water, warm the carafe — or accept that your real brew temperature is several degrees lower than the display.
Last reviewed 8 August 2026