Reading Brewing Water
Water Hardness in Brewing: Calcium, Sulfate, Chloride
In brewing, water hardness describes how much calcium and magnesium are dissolved in the water, along with bicarbonate, sulfate, and chloride. Each of these minerals affects the mash, the bitterness, and the mouthfeel. Here's how to read a water analysis with a brewer's eye.
What does water hardness mean in brewing?
Every water analysis from a local supplier lists a hardness figure, in Germany often given in degrees of German hardness (°dH). One degree corresponds mathematically to 10 milligrams of calcium oxide per liter. What's meant are the dissolved calcium and magnesium salts. Experts distinguish two parts: carbonate hardness is tied to bicarbonate and precipitates out as scale during boiling. Non-carbonate hardness is tied to sulfate and chloride and stays dissolved even after boiling.
For brewers, this distinction matters more than the total figure. Two waters with the same overall hardness can behave completely differently in the brewhouse. If the hardness is mostly carbonate-based, the water raises the pH of the mash. If it's mostly sulfate-based, the calcium tends to lower the pH instead and adds a dry character. The hardness number on the water bill alone can't tell you whether a water suits a pilsner or a porter.
Calcium and magnesium: the helpers in the mash
Calcium is the most important mineral in brewing water. It reacts with phosphates from the malt, releasing acid in the process, which brings the mash pH into the range where enzymes work well. Brewers usually aim for a value between roughly 5.2 and 5.6. Calcium also helps yeast settle out, protects enzymes from heat, and helps proteins flocculate better during the boil, which later yields a clearer beer.
Magnesium works similarly, but more weakly. Yeast needs it in small amounts as a nutrient, and good malt usually supplies enough on its own. In larger amounts, magnesium tastes harsh to bitter and can have a laxative effect, so brewers rarely add it deliberately. Kolbach's residual alkalinity weighs calcium and magnesium against bicarbonate. The higher this residual figure, the more strongly the water pushes the pH upward, and the more likely it needs dark malt or acidification to compensate.
Bicarbonate: the adversary of pale beers
Brewers making pale beers fear bicarbonate above all, often shortened to carbonate. It acts as a buffer against acidity. With pale malt, this pushes the mash pH too high, enzymes work less effectively, and during lautering—separating the wort from the spent grain—more harsh tannins get pulled from the husks. The result can be a dull, bitter beer with a harsh hop character.
Dark and roasted malts flip this equation. They bring enough acidity of their own to offset carbonate-rich water. In very soft water, though, they'd make the mash too acidic, and the beer would taste sharp and sour. This is the chemical core of why cities with carbonate-rich water were historically known for dark beers, and cities with soft water for pale ones.
Sulfate vs. chloride: how water shapes flavor
Sulfate and chloride barely change the pH, but they change how a beer tastes. Sulfate makes hop bitterness drier, firmer, and longer-lasting. Beers brewed with sulfate-rich water finish crisp and sharp. Chloride, on the other hand, emphasizes malt sweetness and makes the mouthfeel fuller and softer. Many brewers pay close attention to the ratio between the two: more sulfate for a dry bitter or a West Coast IPA, more chloride for a soft hazy IPA or a malty dark lager.
Sodium rounds things out in small amounts, but in larger amounts tastes salty, as in gose, which gets its salt as an added ingredient, though. Iron and manganese are unwelcome in brewing water because they taste metallic and interfere with yeast. Chlorine from tap-water disinfection has to be removed before brewing, or it produces medicinal-smelling chlorophenols. With these few variables in mind, you can read any water analysis like a brewer.