Free Distilling Tools

Mash Water Chemistry Calculator

Calculate gypsum, calcium chloride, Epsom salt and baking soda additions for your mash water, and see the resulting mineral profile.

Water Chemistry Calculator

Tell us your target, we'll suggest the salt additions

L
Total mash water volume
▾
Starting point if you don't have a water report
Source water profile (ppm / mg per L)
ppm
ppm
ppm
ppm
ppm
ppm
Your target
ppm
Most mash profiles target roughly 50-150 ppm
ppm
Leave blank to skip Epsom salt entirely
Target sulfate : chloride ratio
: 1
These figures assume salts fully dissolve. Add salts to the mash water before mixing with grain, and stir well to ensure full dissolution.

Brewing salt kit (Gypsum, CaCl2, Epsom): Food-grade salts sized for home batches, the three most commonly used mash water additions.As an Amazon Associate we earn from qualifying purchases.

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Next step: Work out your strike water temperature and grain bill.

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Why Mash Water Chemistry Matters

Mineral content in mash water directly affects mash pH, which in turn affects how well enzymes convert starch to fermentable sugar. Water that is too soft or too hard for a given grain bill can push mash pH outside the range where enzymes work efficiently, reducing conversion and leaving fermentable sugar behind in the mash.

Calcium in particular plays a direct role beyond pH: it helps enzymes stay stable at mash temperatures and assists yeast flocculation later in fermentation. Most all-grain mash profiles benefit from a calcium level in the range of roughly 50 to 150 ppm, though the right target depends on your grain bill and the water you are starting from.

Resulting ppm = Source water ppm + (grams of salt ÷ liters of water) × ion contribution factor

The sulfate and chloride balance affects perceived character rather than conversion efficiency. Sulfate tends to accentuate a drier, more mineral character, while chloride tends to round out mouthfeel. Neither is right or wrong, and the balance that suits a bourbon mash may differ from what suits a lighter, more neutral spirit base.

Choosing Your Salt Additions

Gypsum (calcium sulfate) and calcium chloride are the two most commonly used salts, since both raise calcium while pushing the sulfate-to-chloride balance in opposite directions. Using them together, rather than only one, gives more control over the final ratio than either salt alone.

Epsom salt (magnesium sulfate) is used more sparingly, mainly when magnesium is genuinely low, since yeast needs only a small amount of magnesium and excess levels can contribute a harsh, bitter character. Baking soda and non-iodized table salt are used less often in mash water specifically, more commonly for adjusting pH upward or contributing sodium character in particular recipes.

Start with small additions, a gram or two per batch at typical home scale, and adjust from there once you have tasted the results across a batch or two, rather than dosing heavily on the first attempt based on a target profile alone.

Frequently Asked Questions

No. Water chemistry adjustments matter for all-grain mashing, where mineral content affects starch conversion and enzyme activity during the mash. A sugar wash has no mash step and no grain enzymes to support, so source water mineral content has little practical effect beyond yeast health, which nutrient additions address separately.

Reverse osmosis or distilled water gives you a clean, known baseline of essentially zero minerals, letting you build up exactly the profile you want from salt additions alone. Tap water works too, but its mineral content varies by location and season, so get an actual water report from your supplier rather than guessing, since starting from an unknown baseline makes every calculation downstream unreliable.

There's no single correct ratio, it depends on the character you're after. Higher sulfate relative to chloride tends to accentuate a drier, sharper grain character, while higher chloride relative to sulfate tends to round out mouthfeel and soften perceived bitterness from grain husks. Most all-grain mash profiles for whiskey and rye fall somewhere in a roughly balanced to moderately sulfate-forward range, but this is a matter of taste to dial in over a few batches, not a fixed target.

Chalk is poorly soluble in water and doesn't dissolve reliably without dissolved CO2 present, which most home setups don't have, so measured chalk additions often don't fully go into solution and behave less predictably than the other salts here. If you need to raise alkalinity, pickling lime or baking soda are more predictable options for a home setup.

Indirectly. Water chemistry affects mash pH and enzyme activity, which affects fermentability and how cleanly the mash converts, and it can carry through into wash flavor precursors. It does not survive distillation the way it survives into a glass of beer, since minerals are non-volatile and stay behind in the still, but a healthier mash and fermentation upstream still shows up in the character of what you eventually collect.

With five salts and six ions to control, the full system is generally overdetermined and coupled, meaning an auto-solver targeting every ion at once would frequently demand a negative, impossible amount of some salt. Calcium and the sulfate-to-chloride ratio are the two properties that matter most in practice and can be solved for exactly with just gypsum and calcium chloride. Magnesium is solved separately since only Epsom salt affects it. For sodium, bicarbonate or other fine-tuning, use Enter My Own Amounts to test specific doses directly.

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