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Coffee Brewing Temperatures Explained by James Hoffmann

The Myth of "Burning" Coffee​

The idea that boiling water (100°C) will burn coffee is considered nonsensical by the speaker, as coffee beans are roasted at temperatures above 220°C. Boiling water will not further the roasting process.

However, using very high temperatures to brew very dark-roasted coffee can extract unpleasant, bitter, burnt, ashy, or smoky flavours.

The Experiment: Measuring Slurry Temperature​

The key to the experiment is measuring the temperature of the slurry (the mixture of coffee grounds and water) rather than just the water temperature in the kettle.

1. Pour-Over (V60-style) Test​

  • Method: Boiling water was poured over a preheated brewer with coffee grounds, and a probe measured the slurry temperature.
  • Result: Even with water poured as close to the boil as possible, the slurry temperature never exceeded 91°C (or perhaps 93°C if the water was hotter).
  • Reason: Heat is lost due to several factors: the temperature of the grounds, the ambient environment, and evaporative cooling as steam rises.

2. French Press Test (No Preheating)​

  • Method: Boiling water was added directly to grounds in a non-preheated French press.
  • Result: The temperature of the slurry was again nowhere near boiling.

3. French Press Test (Preheated)​

  • Method: The experiment was repeated with a well-preheated French press.
  • Result: The temperature was only a little bit hotter than the unheated test, demonstrating how difficult it is to get the slurry temperature close to 100°C.

Conclusion and Recommendations​

The video concludes that it is extremely difficult to get the coffee slurry to very high temperatures during a typical brew.

  • For Specialty Coffee (Medium to Light Roasts): Use the hottest water you can get (i.e., straight off the boil). It is very hard to get the temperature wrong with these roasts, and the heat is needed for optimal extraction.
  • For Darker Roasts: If you find the coffee tasting bitter, burnt, or harsh, reduce the brewing temperature. Brewing in the mid-to-high 80s Celsius will yield a smoother, less bitter result while still achieving good extraction. The only exceptions where the water temperature might stay too high are devices like siphons, where you need to pay attention to temperature control.