MEBAK - 1 Water - 1.2 Brewing liquor - 1.2.2 Softening test using lime water

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1.2.2 Softening test using lime water Principle By addition of lime water or milk of lime the hydrogen carbonates and free carbon dioxide are transferred into carbonates and are precipitated to a large extent: Ca(HCO3)2 + Ca(OH)2 → 2 CaCO3 + 2 H2O Mg(HCO3)2 + Ca(OH)2 → MgCO3 + CaCO3 + 2 H2O CO2 + Ca(OH)2 → CaCO3 + H2O Calcium carbonate is indissoluble and precipitates, in contrast magnesium carbonate is soluble to a large extent. A further equivalent Ca(OH)2 transfers the magnesium carbonate into the indissoluble magnesium hydroxide: MgCO3 + Ca(OH)2 → CaCO3 + Mg(OH)2 However, the calculated amount would lead to a lime surplus in the water (pH too high), since for the quantitative precipitation of the magnesium hydroxide a very high alkalinity is required; therefore, the so called “split treatment”-method is preferred, i.e. the quantity of lime water calculated for the total quantity is added to 2/3 of the untreated water, thus, a high surplus of lime results and with it also the magnesium hydrogen carbonate is precipitated. The addition of approx. 1/3 of the untreated water blunts the lime surplus and causes the complete precipitation of calcium hydrogen carbonate. In this manner the carbonate hardness equivalent to calcium is eliminated completely and the carbonate hardness caused by magnesium is eliminated to a large extent. Required analysis values for calculating the lime water quantity

1) CaO content of lime water Reagents Hydrochloric acid, 0.1 N Phenolphthalein, 1 % (alcoholic solution) Procedure - Add phenolphthalein to 20 ml clear (possibly filtrated before) saturated

lime water - Titrate with 0.1 N hydrochloric acid until colourless

MEBAK - 1 Water - 1.2 Brewing liquor - 1.2.2 Softening test using lime water

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Calculation CaO (g/l) = 0.1 N hydrochloric acid (ml) × 0.14 (value a)

2) Determination of carbonate hardness See 1.1.10.3 (value b)

3) Determination of required lime water quantity for precipitation of free carbon dioxide

Reagents Hydrochloric acid, 0.1 N Phenolphthalein, 0.0375 % (alcoholic solution) Clear saturated lime water (as in 1.) Procedure - Add 1 ml phenolphthalein to 200 ml of brewing liquor to be softened in

ball-neck-flask - Titrate to light pink colouring persisting for 3 min (value c) while carefully

swivelling

4) Determination of magnesium hardness

Reagents and procedure See 1.1.14 Calculation Mg-hardness (°d) = Mg2+ (mg/l) × 0.2303 (value d)

5) Desired residual carbonate hardness (value e) Calculation of lime water quantity to be added per hl brewing liquor

Lime water (l/hl) = ca

edb +

−+

Remarks Lime water is defined as clear saturated solution of calcium hydroxide. The solubility depends on water temperature and is overall low. Maximum dissolution at 10 °C 1.38 g/l, at 30 °C 1.20 g/l (pH 12.4).