Concentrate · steep · dilute
Cold brew calculator
Coffee and water for a batch of concentrate, when to strain it, roughly how much you will get, and how far to dilute it.
Your batch
- Coffee200 gabout 2½ level cups (approximate), coarsely ground
- Cold water1,000 ml33.8 fl oz · 4¼ cups
- Strain at12:00next day, after 16 h
- Concentrateabout 504 ml17 fl oz, a rough estimate
- To drinkabout 1,008 ml1 part concentrate to 1 part water: about 4.3 drinks of 237 ml
Diluted like this, it is roughly as strong as coffee brewed at 1:10. To match the SCA’s standard brew ratio of 55 g per litre (1:18.2), add about 2.6 parts water to each part of concentrate, or less if you like it stronger.
Making a concentrate
Cold brew steeps coarsely ground coffee in cold or room-temperature water for many hours, then strains it. Making it strong, as a concentrate, keeps the batch small; you dilute each glass to taste. The ratio is grams of water per gram of coffee, and 1 ml of water weighs about 1 g. The ratios and steep times here are common starting points rather than any standard, so change one thing at a time between batches.
“Concentrate” is a rough estimate of what you get after straining: the grounds keep back about 2.5 g of liquid per gram of coffee, a figure measured for immersion brewing in a laboratory, and more if you do not let them drain. “Diluted like this” uses the same study’s finding that a brew’s strength goes roughly with its ratio, so one part of a 1:5 concentrate with one part water is about as strong as a 1:10 brew.
Keep it clean and cold. Wash your hands and everything you use before you start, and keep the strained concentrate covered in the fridge; steeping in the fridge is the cautious choice too. Researchers at the University of Georgia found that harmful bacteria, if they get in, can survive in cold brew for days, and some for weeks. No food-safety body publishes a keep-by time for home cold brew, so use your own judgement and throw it out if it smells or tastes off.
Sources
- Water kept by the grounds, 2.48 ± 0.19 g per g of coffee, and strength roughly inversely proportional to the water-to-coffee ratio: Liang J, Chan KC, Ristenpart WD. An equilibrium desorption model for the strength and extraction yield of full immersion brewed coffee. Scientific Reports 11, 6904 (2021).
- 55 g of coffee per 1.000 kg of water as the SCA’s standard brew ratio (1:18.2): SCA Standard 310-2021, Home Coffee Brewers (Specialty Coffee Association, 2022; archived copy).
- Bacteria surviving in cold brew, hygiene and refrigeration: Can cold brew coffee make you sick?, University of Georgia College of Agricultural and Environmental Sciences (30 January 2024).
- Ratios of 1:4 to 1:8 and steeps of 12 to 24 hours are common starting points used by home brewers, not figures from these sources.
Questions
How long does cold brew concentrate keep?
No food-safety agency gives a keep-by time for home cold brew. Keep it covered in the fridge, make it with clean equipment and clean hands, and use your judgement: if it smells or tastes off, pour it away.
Why did I get less concentrate than the water I used?
The wet grounds hold on to some of it. At 1:5 a litre of water with 200 g of coffee loses roughly 500 ml that way, which is why the calculator shows about half a litre of concentrate. Pressing or draining the grounds longer gets a little more out.
How much should I dilute it?
Start with one part water or milk to one part concentrate and adjust to taste. The calculator also shows how far you would dilute it to match the strength of filter coffee at the SCA’s standard ratio.