Water salts: gypsum, calcium chloride and others
How much salt to add to the water to hit the target profile.
Water is more than ninety percent of beer, and its ion composition noticeably affects both the taste and the course of the mash. The calculator takes the profile of your water and a target profile, works out how many grams of each salt to add to the volume, and shows what came out. An exact match on all six ions never happens: every salt drags a second ion along, so the profile is fitted as closely as the salts allow. Mash pH is not calculated here — it also needs the malt composition.
Calculator
An empty field means “I don’t know”: it counts as zero in the calculation.
How to add ions
The same target for sulfates or chlorides can be reached with different salts: the second ion comes along for free — calcium, magnesium or sodium. Choose by which one you need more.
Fill in the volume and the water composition — yours and the target — then press “Calculate”.
Why touch the water
The ions in water are not “tasty” in themselves, but they set the background: sulfates emphasise hop bitterness, chlorides add malt fullness, and sodium in small amounts softens the flavour. Calcium is needed by the mash enzymes and the yeast, while bicarbonate makes the mash more alkaline and pushes the pH up.
Most brewers do not calculate their water, and that is fine: salts are a refinement, not a mandatory step. If the water tastes good, is not too hard and does not reek of chlorine, you can brew as it is. The calculator is needed when you want to reproduce a style deliberately: soft water for a pilsner, more sulfate-rich water for an IPA, more alkaline water for a stout.
Enter the six numbers from a water report — or leave the fields empty. An empty field means “I don’t know”, and in the calculation it counts as zero: the result will be approximate, but the page will not demand something you do not have.
How we calculate
Each salt, once dissolved, releases strictly defined ions: gypsum gives calcium and sulfates, calcium chloride gives calcium and chlorides, and so on. Knowing the mass of the salt and the volume of water, the addition to the concentration is found by division: milligrams of ion per gram of salt divided by the litres.
The calculator selects the salt masses so that the final profile comes as close to the target as possible, and it never subtracts ions: salts only add them. If the source water already has more of an ion than the target, the fit leaves an excess — it shows up in the deviation. That is why matching all six ions at once is impossible: gypsum, for instance, raises both calcium and sulfates, and in hitting the sulfate target it easily pushes calcium out of range.
Small discrepancies are normal. Taste changes gradually, and a difference of ten or twenty milligrams per litre is usually imperceptible. The order of magnitude and the sulfate-to-chloride ratio matter far more.
Final_i = Source_i + Σ (m_salt · k_salt,i) / V where m is the salt mass, g; k is the salt’s contribution to the ion, mg/g; V is the water volume, L
What each salt contributes
| Salt | What it adds |
|---|---|
| Gypsum, CaSO₄·2H₂O | calcium and sulfates: a dry, hoppy aftertaste |
| Calcium chloride, CaCl₂·2H₂O | calcium and chlorides: a full, malty aftertaste |
| Epsom salt, MgSO₄·7H₂O | magnesium and sulfates; magnesium is needed by the yeast |
| Magnesium chloride, MgCl₂·6H₂O | magnesium and chlorides; needed less often than Epsom salt |
| Table salt, NaCl | sodium and chlorides; sodium softens the flavour but quickly turns salty |
| Baking soda, NaHCO₃ | sodium and bicarbonate: raises alkalinity and mash pH |
| Chalk, CaCO₃ | calcium and carbonate; dissolves poorly, especially on boiling |
Residual alkalinity and mash pH
The alkalinity of water neutralises the acidity of the malt. The difference between them is described by residual alkalinity: the contribution of calcium and magnesium, which on the contrary acidify the mash, is subtracted from the total alkalinity.
The higher the residual alkalinity, the more the water raises mash pH. For pale beer the aim is zero or a small positive value: then the malt itself sets the required acidity. Dark malts are more acidic, so dark beer tolerates, and sometimes requires, more alkaline water. A negative residual alkalinity means the water acidifies the mash: for very pale malt that can be useful, for dark malt harmful.
The calculator deliberately does not compute mash pH. It depends not only on the water: the acidity and buffering capacity of the malt, the share of dark and roasted grains, the water-to-grain ratio and even the crush shift it more than the salts do. An honest estimate of pH requires a grist model, and without one any number would be a fabrication. pH is measured with a pH meter ten to fifteen minutes after the start of the mash, not calculated from the water.
RA = Alk − (Ca / 3.5 + Mg / 7) where Alk is alkalinity in mg/L CaCO₃ (for bicarbonate, Alk ≈ HCO₃ · 0.82); Ca and Mg are in mg/L
What the calculator does not do
- It does not remove ions: salts only add. If the water already has more sulfates or sodium than the target, they cannot be lowered with salts — only dilution with low-mineral water or reverse osmosis helps.
- It does not compute mash pH and does not select an acid: that needs the grist composition and its acidity.
- It does not select salts to taste: sulfates and chlorides affect the perception of bitterness, but the recipe, the hops and the yeast matter no less.
- It does not account for the fact that some salts precipitate or bind to other ions: the calculation uses the nominal composition, and the real profile may differ.
- It does not replace a water analysis: the numbers in a water utility report are averaged over the season and the network, not over your glass.