Water Chemistry
Water is more than 90% of finished beer, and it is never just H₂O. Dissolved minerals ride along from your tap: calcium, magnesium, sodium, chloride, sulfate, and bicarbonate. Each one changes how the beer mashes, ferments, and tastes. This is why the same grain and hops can come out sharp and dry from one water and soft and round from another. It is one of the biggest levers you have over a recipe.
This page walks through what each ion does, the chloride-to-sulfate ratio that steers the malt-versus-hop balance, how alkalinity ties into mash pH, the handful of salts brewers use to hit a target, and how the math actually gets done.
What the Ions Actually Do
Six ions matter for brewing. Two of them (chloride and sulfate) drive flavor directly, calcium does most of the chemical work, and bicarbonate governs pH. Here is what each one brings, and the rough range brewers aim for.
Calcium (Ca²⁺) : the workhorse. It drives mash enzyme activity, helps yeast stay healthy and flocculate for clearer beer, and lowers mash pH by reacting with malt phosphates. Most brewers want at least 50 ppm. 50–150 ppm is the usual range.
Magnesium (Mg²⁺) : a yeast nutrient and a minor mash acidifier, but it turns sour and astringent when there is too much. Malt already supplies plenty, so you rarely need to add it. 10–30 ppm.
Sodium (Na⁺) : rounds out and lifts malt character at low levels, the way a pinch of salt does in cooking. Above roughly 100 ppm, especially alongside sulfate, it turns harsh and briny.
Chloride (Cl⁻) : accentuates malt sweetness, body, and a fuller, rounder mouthfeel. One half of the flavor ratio below. Comfortable up to around 150 ppm.
Sulfate (SO₄²⁻) : sharpens and dries out hop bitterness, making it crisp and assertive. The other half of the ratio. Pale hoppy styles often run 150–350 ppm.
Bicarbonate (HCO₃⁻) : alkalinity, the water's resistance to a drop in pH. High bicarbonate pushes mash pH up. That is a problem for pale beers and a help for dark ones, where roasted malts would otherwise drive pH too low.
The Cl:SO₄ Ratio
The balance between chloride and sulfate is the single most impactful water-chemistry metric for flavor. It sets the tug-of-war between malt fullness and hop crispness:
| Cl:SO₄ | Character |
|---|---|
| < 0.5 | Very hoppy: dry, crisp bitterness |
| 0.5–0.8 | Hop-forward, balanced toward bitterness |
| 0.8–1.2 | Balanced |
| 1.2–2.0 | Malt-forward, softer, rounder |
| > 2.0 | Very malty: full, sweet character |
As a rule of thumb, hop-forward styles run sulfate-heavy (a West Coast IPA might sit near 0.4:1), while malty styles run chloride-heavy (a Scottish ale near 2:1). Treat it as a lever, not a law. Plenty of good beers ignore the “ideal” ratio for their style, and it is worth trusting your own palate over the chart.
Alkalinity and Mash pH
Bicarbonate is the source of your water's alkalinity: its ability to resist a drop in pH. Grain is acidic, so the mash naturally wants to pull pH down, and alkalinity fights that. Calcium and magnesium work the other way, reacting with malt phosphates to release acidity. This balance is Kolbach's residual alkalinity, with calcium counting a little over three times as much as magnesium. High- bicarbonate water pushes mash pH up, which is why pale beers on hard water often need acid, and why dark beers can carry alkalinity that would wreck a pale ale. The mash pH article covers how that is predicted and corrected in detail.
The Brewing Salts
To move your water toward a target, brewers reach for a handful of food-grade salts. Each one adds specific ions at a known rate per gram per liter:
| Salt | Adds |
|---|---|
| Gypsum (CaSO₄) | Ca + SO₄ |
| Calcium Chloride (CaCl₂) | Ca + Cl |
| Epsom Salt (MgSO₄) | Mg + SO₄ |
| Table Salt (NaCl) | Na + Cl |
| Baking Soda (NaHCO₃) | Na + HCO₃ |
Gypsum and calcium chloride do most of the work, since between them they cover calcium, sulfate, and chloride: the ions that steer flavor most. Epsom salt and table salt are used sparingly. Baking soda adds alkalinity, but bicarbonate is more often handled with acid on the other side, so it comes out mostly for dark beers that need the pH headroom.
Calculating Your Additions
Adjusting water is a subtraction problem with a catch. You start with your source profile (or near-zero, if you build up from RO or distilled), pick a target, and the gap between them is what the salts have to close. The catch is that no salt moves a single ion. Gypsum raises calcium and sulfate. Calcium chloride raises calcium and chloride. So you cannot tune one number in isolation: reaching your sulfate target with gypsum drags calcium up with it, and topping up calcium might overshoot chloride.
Brewers have traditionally worked this out in a spreadsheet: add a pinch of one salt, watch all six ions move, back off another, and repeat until every number is close enough. There is rarely a perfect answer. “Close on all six” is the realistic goal, and then you split the total between mash and sparge water by volume.
Letting the Builder Do the Math
That whole juggling act is what the recipe builder handles for you. Set your source water and a target (a BJCP style preset that matches your recipe, or a custom profile), and it shows where every ion sits against the target, then solves for the salts in one pass.
Bounded least squares
unique to Brewing.ItInstead of trial and error, we solve the coupled-ion problem directly. Finding the combination that gets all six ions as close to the target as possible, without any salt going negative (you cannot remove salt), is a weighted least-squares optimization with bounds. Chloride and sulfate carry more weight, because the Cl:SO₄ ratio has the biggest impact on flavor.
Smart rounding
Nobody measures 9.47g of gypsum. After solving, we round to 0.1g increments, but we don't just round each salt independently. We test all possible floor/ceil combinations and pick the one that minimizes total ion error. This matters because rounding one salt up might offset rounding another down.
Mash & sparge splits
The builder splits your total salt additions proportionally between mash and sparge water based on their volumes. This gives you the exact grams to add to each pot.
And because your water feeds mash pH, changing your salts updates the predicted mash pH live. If it lands outside the 5.2–5.6 range, the builder tells you how much acid or baking soda to add to bring it back.