How this calculator works
Cold brew is made by steeping coarse ground coffee in cold water for 12 to 18 hours, then filtering out the grounds. Because no heat is used, the result is usually brewed strong as a concentrate and diluted with water or milk before drinking. The recipe is written as a ratio of water to coffee by mass: 1:5.3 means 5.3 grams of water for every gram of coffee. The grounds absorb about one millilitre of water for every gram at a coarse cold brew grind, so the concentrate you end up with is less than the water you started with. That is why the calculator works back from the concentrate volume: grounds = concentrate / (ratio - 1), and water = grounds x ratio. A finer grind, a longer steep or a warmer room all extract more, but the ratio is the place to start - and a fine grind holds more water, so the yield falls.
Formula
grounds (g) = concentrate (mL) / (ratio - 1). water (mL) = grounds x ratio. concentrate = water - 1 mL per gram of grounds. cups after dilution = concentrate / (1 + parts) / 240, where parts is 1 for equal parts, 2 for one part concentrate to two parts water and 0 for no dilution.
Worked example
One litre of concentrate at the regular ratio of 1:5.3 needs 1000 / (5.3 - 1) = 232.6 g of grounds and 232.6 x 5.3 = 1232.6 mL of water. The grounds retain about 232.6 mL, so the batch yields 1232.6 - 232.6 = 1000 mL of concentrate. Served at 1:1, one litre makes 1000 / 2 = 500 mL of drink, a little over two 240 mL cups.
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Frequently asked questions
Why is cold brew concentrate so strong?
A concentrate is meant to be diluted. Brewing at 1:5 means the liquid that drips out is several times the strength of a normal cup, so it keeps longer and travels well. Diluting it at serving time gives a normal drink and lets each person choose their strength.
How long should I steep it?
Most cold brew steeps for 12 to 18 hours in the fridge, or 8 to 12 hours at room temperature. Longer steeping extracts more but also pulls out more bitterness from the grounds; a very fine grind can turn muddy. Start at 16 hours in the fridge and adjust.
Why does the recipe subtract the water held by the grounds?
Spent coffee grounds hold on to roughly one millilitre of water per gram at a coarse grind, and more at a fine grind. That water is in the batch but does not reach the jug, so a recipe that ignores it produces less concentrate than planned. The subtraction turns the water and grounds into the volume you actually get.
How much caffeine is in cold brew?
It depends on the ratio, the dose and the steep, and a concentrate can carry several times the caffeine of a similar volume of drip coffee. Diluted at 1:1, a 240 mL cup made to the regular ratio is in the range of a strong cup of coffee. Pregnant people and children should follow the Health Canada daily limits.