Residual alkalinity (RA)
Term from the Brauwerkstatt brewing glossary, category “Brewing water and pH”.
Explanation
What is left of the acid buffer once calcium and magnesium work against it in the mash: RA = alkalinity − (Ca / 1.4 + Mg / 1.7), all in mg/l (alkalinity as CaCO₃). It shows how strongly the water raises mash pH overall.
Work it out yourself
Brewing water calculator – Adjust your tap water to the beer style: the calculator tells you how much calcium chloride, gypsum and lactic acid you need.
Test your knowledge
What does the residual alkalinity of brewing water describe?
- How much chlorine the water contains
- How strongly the water raises the mash pH
- How warm the water is
Show answer
Correct: How strongly the water raises the mash pH. High residual alkalinity suits dark beers; for pale beers it is lowered with lactic acid or soft water.
Frequently asked questions
Do gypsum and calcium chloride raise alkalinity?
No. The salts add calcium, sulphate and chloride, but no bicarbonate. Alkalinity stays the same; general hardness rises. In the mash, the calcium does lower residual alkalinity.
Can you taste a few mg/l of residual alkalinity?
No. About 18 mg/l of residual alkalinity shifts mash pH by only about 0.03, which is below the accuracy of typical pH meters.