Blame the scoop
If your coffee is weak one day and harsh the next, the scoop is the usual suspect. The same level scoop can hold anything from about 7 g to 10 g of coffee, depending on the roast and the grind. That's a swing of about 40% in strength from a scoop that looks identical.
A kitchen scale fixes it. Weigh the coffee and the water, and a cup you like becomes a recipe you can repeat.
Dial 1: the ratio
For filter, pour-over or French press, the starting point is about 1 g of coffee for every 16 g of water (and 1 g of water is 1 ml). Espresso is a different, much stronger recipe.
| You're making | Coffee | Water |
|---|---|---|
| One mug | 15 to 16 g | 250 ml |
| Two mugs | 30 to 32 g | 500 ml |
| A litre jug | About 60 g | 1 litre |
Treat it as a starting point: once your cup tastes right, keep the numbers and you can repeat it every day.
Dial 2: water temperature
Brew just off the boil, at about 90 to 96°C. You don't need a thermometer: boil the kettle and let it rest about 30 seconds.
Much cooler water can't pull enough flavour out, and the cup tastes sour and thin. And since a cup of coffee is about 98% water, use water that tastes good: if your tap water tastes of chlorine, so will the coffee.
Dial 3: the grind
Grind size sets the speed. Finer grounds have more surface, so the flavour comes out faster; coarser grounds give it up slowly.
| Grind | Looks like | Used for |
|---|---|---|
| Fine | Table salt | Espresso |
| Medium | Sand | Filter and pour-over |
| Coarse | Sea salt | French press |
Grind just before you brew if you can. Much of the aroma fades within about 30 minutes of grinding.
Read the taste: sour or bitter
Here's the idea that makes the grind useful. Water pulls flavour out of coffee roughly in order: acids first, then sweetness, then bitterness. Real brewing overlaps, but as a rule of thumb it works:
- Stop too early (too coarse, too short, too cool) and you get mostly acids: the cup is sour and thin. Try grinding finer.
- Go too far (too fine, too long) and the bitterness takes over: the cup is bitter and harsh. Try grinding coarser.
The sweet spot is in between.
| The cup tastes | What happened | Change |
|---|---|---|
| Sour, thin | Probably too little came out | Try finer (and check the water is hot enough) |
| Bitter, harsh | Probably too much came out | Try coarser |
| Weak but not sour | Not enough coffee | Weigh it: about 60 g per litre |
Common mistakes
- Adding more coffee to fix a sour cup. It makes it stronger, but still sour. Fix the grind first, then weigh.
- Grinding coarser when it's sour. That slows extraction down even more, so the cup gets more sour.
- Changing three things at once. Move one dial, one notch at a time, so you know which change worked.
- Pouring at a rolling boil or with hot tap water. Aim for just off the boil.
Questions people ask
How much coffee per cup?
About 15 to 16 g of coffee for a 250 ml mug, a ratio of roughly 1:16. For a litre, about 60 g.
What temperature should water be for coffee?
About 90 to 96°C, just off the boil. Let a boiled kettle rest about 30 seconds.
Why does my coffee taste sour?
Usually too little flavour came out of the grounds, so the acids dominate. Try grinding finer first, and make sure the water is just off the boil, not much cooler.
Why does my coffee taste bitter?
Usually too much came out: the water got past the sweetness to the bitter compounds. Try grinding coarser, one notch at a time.
