Cold brew is the most forgiving method and the easiest one to ruin with a bad ratio. The confusion comes from two different products sharing one name: a concentrate you dilute, and a ready-to-drink brew you pour straight. They need different numbers. Pick which one you are making before you grind anything.
The two ratios that matter
A cold brew concentrate is brewed somewhere between 1:5 and 1:8. You then dilute it 1:1 to 1:3 with water or milk before drinking. That means the cup you actually drink lands around 1:15 to 1:17 — roughly the same strength as filter coffee, which is the whole point.
A ready-to-drink cold brew is brewed at 1:12 to 1:17 and consumed as-is. No dilution. It takes more fridge space and more coffee per litre, but it removes a step and eliminates the risk of someone at your house making it wrong.
| Style | Brew ratio | Dilution | Final strength |
|---|---|---|---|
| Concentrate, strong | 1:5 | 1:2 | ~1:15 |
| Concentrate, standard | 1:8 | 1:1 | ~1:16 |
| Ready to drink | 1:12 | none | 1:12 |
| Ready to drink, light | 1:17 | none | 1:17 |
Grams for real batch sizes
The table below assumes a concentrate at 1:8 that you will dilute 1:1. If you want ready-to-drink, move up to the concentrate column and treat the result as final.
| Batch | Coffee | Water | Yield after dilution |
|---|---|---|---|
| 500 ml | 55 g | 440 g | ~1 L |
| 750 ml | 83 g | 665 g | ~1.5 L |
| 1 L | 111 g | 890 g | ~2 L |
| 2 L | 222 g | 1778 g | ~4 L |
Grind size
Coarse. Coarser than French press, roughly the texture of raw sugar or coarse sea salt. Too fine and you get a muddy cup that clogs filters and takes twenty minutes to strain. Too coarse and the brew tastes hollow and woody, like tea made from sawdust.
If you own a grinder with numbered settings, cold brew usually sits two to four clicks coarser than your French press setting. Write the number down once you find it — cold brew is the one method where repeatability beats experimentation.
Time and temperature
Cold water extracts slowly. Sixteen hours at room temperature, or eighteen to twenty hours in the fridge. Room temperature pulls more sweetness and more acidity; the fridge is cleaner and more forgiving if you forget about it.
Past 24 hours the brew starts pulling bitter, papery compounds and the cup goes flat. Set a timer. This is the single most common cold brew mistake — not ratio, not grind, just leaving it too long.
| Temperature | Time | Character |
|---|---|---|
| Room (~21C) | 14-16 h | Sweeter, rounder, more body |
| Fridge (~4C) | 18-20 h | Cleaner, brighter, thinner |
| Fridge | 24 h+ | Bitter, papery, flat |
What to do with the grounds
Strain twice. First through a mesh sieve or the filter basket, then through a paper filter or a clean cloth. The second pass removes the fine silt that makes cold brew feel chalky in the mouth.
Do not squeeze the filter to get the last drops. The liquid you force out is heavily loaded with fines and bitterness. Let it drip and accept the small loss.