Step 3 · Heat
Water: temperature, stability and what to brew with
A cup of coffee is about 98% water. Its temperature sets how fast flavor extracts, and its minerals decide which flavors come out. Both are easy to get right once you know what matters.
Temperature
Hotter water extracts faster. Too cool, and you pull out mostly the quick-dissolving acids: the cup tastes sour, thin and flat. Too hot, and you drag out harsh, drying bitterness along with everything good. Most pour-over is brewed between about 90–96°C, just below boiling.
- Light roasts: 94–96°C. They're dense and slow to extract, so they need the extra energy.
- Medium roasts: 91–94°C.
- Dark roasts: 88–91°C. They extract easily, and cooler water keeps bitterness in check.
No thermometer? Bring the kettle to a boil and let it sit, lid open, for about 30 seconds for a medium roast, or pour almost straight off the boil for a light roast.
Altitude
Water boils at a lower temperature the higher you go, roughly 1°C (about 2°F) less for every 300 m (1,000 ft). At 2,000 m it boils at around 93°C. At altitude, "just off the boil" is already cooler than the target, so brew straight off the boil and grind a touch finer.
Why stable temperature matters
The number on your kettle isn't the temperature your coffee actually brews at. Water cools as it leaves the spout, cools again on contact with the dripper and grounds, and the kettle itself cools between pours. The slurry in the dripper is often several degrees cooler than the kettle.
That doesn't matter much if it's the same every time. Consistency is what makes a recipe repeatable. A few habits help:
- Preheat everything. Rinsing the paper filter with hot water also warms the dripper and server. This matters most for heavy ceramic or glass drippers, which soak up heat.
- Use a temperature-controlled kettle if you can. It holds a set temperature on its base between pours, instead of drifting down.
- Keep the lid on between pours, and don't leave the kettle sitting for minutes mid-brew.
- Brew enough water. A nearly empty kettle cools much faster than a full one, so heat a little more than you need.
Kettles
A gooseneck kettle has a long, thin spout that lets you pour a slow, steady, precise stream. You can control where the water lands and how much it stirs the grounds. That control matters more for pour-over than almost any other piece of gear except the grinder.
- Electric with temperature control: the easiest. Set it once, and it holds the temperature.
- Electric without control: boil, then wait to cool as above.
- Stovetop gooseneck: works fine with a clip-on or probe thermometer.
What water to use
Pure water is surprisingly bad at brewing coffee. Dissolved minerals do a lot of the extracting, and others change how acidity tastes. The minerals that matter most:
- Magnesium and calcium (hardness) help pull flavor compounds out of the coffee. Too little, and the cup is flat and under-extracted. Too much, and it tastes chalky and dull, and scale builds up in your kettle.
- Bicarbonate (alkalinity) acts as a buffer that neutralises acids. A little keeps coffee from tasting sharp. Too much flattens all the brightness and fruit.
- Chlorine and chloramine, used to disinfect tap water, add medicinal or swimming-pool flavors and should be removed.
For reference, the Specialty Coffee Association's water standard aims for roughly 150 mg/L of total dissolved solids (anything from about 75–250 is acceptable), calcium hardness around 50–70 mg/L, alkalinity around 40 mg/L, a neutral pH, and no chlorine. You don't need to hit these exactly. They show the kind of water to look for: moderately mineralised, not too hard, and clean-tasting.
Practical options
- Filtered tap water: the best starting point for most people. A carbon pitcher filter removes chlorine and improves taste. It removes chloramine less effectively, and doesn't change hardness much.
- Bottled spring water: check the label for moderate mineral content (around 50–150 mg/L dissolved solids) and low sodium. Very mineral-heavy waters are better for drinking than for brewing.
- Mineral packets added to distilled water: the most consistent option, popular with enthusiasts. You get the same water anywhere.
- Avoid distilled or reverse-osmosis water on its own: with no minerals, it brews flat, hollow coffee.
- Avoid softened water: home water softeners swap calcium and magnesium for sodium, which brews poorly and can taste salty.
Simple test: if your water tastes good on its own, it'll brew good coffee. If it tastes of chlorine, metal or chalk, so will your cup.
Kettle care
- Descale regularly if your water is hard. Boil a solution of citric acid (or a few spoonfuls of white vinegar) in water, let it sit, then rinse well.
- Use fresh water. Water left in the kettle for days picks up flat, stale flavors.