CremaTheory

Water recipe

Coffee is over 98% water, and the minerals in it decide what gets pulled out of the grounds. Bicarbonate (alkalinity) neutralizes acids, so too much tastes flat and too little tastes sharp. Calcium and magnesium (hardness) help extract flavor, and too much of them scales your machine. If you start from distilled or RO water, you set both yourself. Enter the targets and you get the grams.

Add to 1 L of distilled or RO water

SaltPer literBatch

What ends up in the water

Ionmg/L (ppm)

Dissolved solids

How it's worked out

  1. Assumes the starting water is 0 ppm. Measure your RO or distilled water; if it reads above ~5 ppm, the result will be off by that much.
  2. SCA Water Standard, from the SCAA Water Quality Handbook (2011): TDS 150 mg/L (75–250), hardness 68 mg/L as CaCO₃ (17–85), alkalinity at or near 40 mg/L, sodium at or near 10 mg/L, pH 7.0 (6.5–7.5). The chart says “calcium hardness”; we apply it to total hardness (Ca + Mg), as most recipe writers do. That reading is common, not settled.
  3. The SCA standard does not specify a Ca:Mg split. Some writers prefer magnesium for extraction. Calcium is more prone to scale in espresso boilers. None of this is settled, so the split is yours and 50% is only a starting point. Gypsum dissolves slowly; stir or shake until clear.
  4. With three salts, alkalinity and hardness (plus the split) fix every gram, so TDS follows from them. We show the result against your target instead of quietly bending one of the others. “Ion sum” counts every dissolved ion. “Evaporated residue” uses the lab convention (dried at 180 °C, where bicarbonate breaks down to carbonate). A TDS pen reads conductivity and multiplies by a fixed factor, so its reading will match neither exactly.
  5. Using baking soda for alkalinity also adds sodium: 40 mg/L of alkalinity brings about 18 mg/L Na, which is above the SCA's “at or near 10”. Potassium bicarbonate avoids this. Whether small amounts of sodium are noticeable in the cup is disputed.
  6. Molar masses are computed from standard atomic weights: NaHCO₃ 84.006, KHCO₃ 100.114, MgSO₄·7H₂O 246.466, CaSO₄·2H₂O 172.164, CaCO₃ 100.086 g/mol. Use USP/food-grade salts. Epsom salt must be plain, not scented.