What you need:

• 400 ml (filtered) water

• 100 g coarsely ground coffee

• (filtered) water or milk to serve

• A pinch of salt - optional

How to make:

• Pour cold filtered water over the grounds. Optionally: add the pinch of salt and stir once to combine. Do not stir again.

• Steep in the fridge Cover and place in the refrigerator. Steep for 16-20 hours.

• Pour the concentrate through a metal mesh filter or french press to remove the bulk of the grounds.

• Pass the liquid through a paper or cloth filter into your storage vessel. This second pass removes fine particles.

• Pour equal parts concentrate and cold water or milk over a large ice cube.

• Taste and adjust, a touch more water opens it up, a touch less keeps it bold.

Notes:

• Grind: French press coarseness or slightly coarser. This is the most important variable; too fine means bitter astringency that no amount of dilution will fix.

• Storage: The concentrate keeps for up to 10 days in the fridge. Flavour often improves on day 2.

• Scaling: Keep the 1:4 coffee-to-water ratio and the method stays the same whether you're making one glass or a full batch.