Coffee Water Recipe Calculator
Distilled water, Epsom salt for hardness, baking soda for alkalinity. Set a batch and two targets and read the grams, or the millilitres of concentrate that a kitchen scale can actually handle.
The SCA's published range for hardness is 50 to 175 ppm, with alkalinity at or near 40.
0.33g
magnesium sulfate heptahydrate, straight into the batch
0.13g
sodium bicarbonate, straight into the batch
Make two stocks once: 2.46 g of Epsom salt in 1 L of distilled water for hardness, and 1.68 g of baking soda in another litre for alkalinity. Each is 1000 ppm, so a millilitre per litre is one ppm.
For 2 L at 68 ppm hardness and 40 ppm alkalinity: 0.33 g of Epsom salt and 0.13 g of baking soda in distilled water. Those are too small for a kitchen scale, so make the two concentrates below and measure 136 ml of one and 80 ml of the other instead.
How to Use This Calculator
- Set the batch in litres. A US gallon is 3.79 L.
- Set the hardness (GH) and alkalinity (KH) you want, in ppm as calcium carbonate, or pick a target.
- Read the salts. The grams straight into the batch are exact and usually too small to weigh, so the tool also gives the same water by concentrate.
- Make the two stocks once. A litre of each keeps in the fridge for weeks, and from then on a batch is two measured pours of concentrate topped up with distilled.
Why Make Water
Coffee is mostly water, and water is not neutral. Magnesium and calcium pull flavour compounds out of the grounds; bicarbonate buffers acidity and, past a point, flattens it. Tap water can be anywhere from nearly empty to hard enough to scale a boiler in a season, and it changes with the season. Distilled or reverse-osmosis water plus two cheap salts gives the same water every time, which is the only way to know whether a change in the cup came from the coffee.
The Two Salts
Epsom salt is magnesium sulfate heptahydrate. One gram in a litre reads as about 406 ppm of hardness as calcium carbonate, so a target of 68 ppm wants 0.17 g per litre. Baking soda is sodium bicarbonate. One gram in a litre reads as about 596 ppm of alkalinity, so 40 ppm wants 0.07 g per litre. Both are food grade from any grocery or pharmacy; use plain Epsom salt with no fragrance.
Those weights are why the concentrate method exists. A kitchen scale that reads to 0.1 g cannot measure 0.07 g. It can measure 2.46 g and 1.68 g into a litre each, and once those stocks exist, a millilitre of either per litre of batch is one ppm. Sixty-eight millilitres of the hardness stock and forty of the alkalinity stock in a litre, topped up with distilled, is the SCA target.
Targets
The Specialty Coffee Association's published standard puts hardness between 50 and 175 ppm with 68 as the target, alkalinity at or near 40, and total dissolved solids around 150. The SCA recipe here reads at about 149 ppm TDS, which is a useful check that the arithmetic is right. Lower alkalinity lets more of a coffee's acidity show, which suits light roasts and pour-over; higher hardness pushes extraction and body. Espresso machines are the reason to stay inside the range: hardness above it scales the boiler, and very low alkalinity with any chloride is corrosive. Water for a machine is a topic in its own right, and we would rather you read the manufacturer than us.
The kettle we use holds temperature well enough that water is the variable we adjust most, and our note on cleaning and maintaining equipment covers what hard water does to it over time.