Lesson 2 - Brewing Water Sources and Treatment

Certain minerals will readily dissolve in water. This contributes to the ‘hardness’ of the water.

Hard water has a high mineral (or ion) content. This mainly consists of the salts of calcium and magnesium cations, along with bicarbonate, carbonate, sulphate, chloride or nitrate anions (total hardness). 

An ion is an atom, or group of atoms, that has a net positive charge (cation) or negative charge (anion).

Water hardness can be split into permanent hardness and temporary hardness.

Total hardness = permanent hardness + temporary hardness

Permanent hardness cannot be removed (precipitated out) by boiling. It consists of the non-carbonate salts such as sulphates, chlorides and nitrates of calcium or magnesium. The removal of permanent hardness is achieved by using an ion exchange column (the details of this will be covered in the lesson discussing water treatment within the brewery).

Temporary hardness can be removed by boiling as the carbonate or bicarbonate salts of calcium or magnesium precipitate out. Another method to remove temporary hardness is by adding calcium hydroxide [Ca(OH₂)], which precipitates calcium and magnesium carbonates.

The ‘hardness’ of a water source can be tested quickly by using soap in water. Hard water collapses soap lather as it forms insoluble salts of fatty acids, which then precipitate. If you can get a good lather of soap bubbles in the water, the water is ‘soft’. If you struggle to form a lather of soap bubbles, then the water is ‘hard’.

Does water hardness matter? Well, water with high levels of hardness causes scaling in water and hot water installations – so this can foul hot water pipes and the heating surfaces of the kettle. This then leads to reduced heat transfer efficiencies.

The minerals making up water hardness can affect the pH of mash and wort. This is because the ions causing temporary hardness generally raise the pH, whilst the ions causing permanent hardness tend to lower pH.

The following equations, using calcium bicarbonate [Ca(HCO₃)₂] as an example, help to explain the effect that temporary hardness can have on wort:

(Equation 1)

Ca(HCO₃)₂ ↔  CaCO₃ ↓  + H₂O + CO₂ ↑                                           

(Equation 2)

Ca(HCO₃)₂ ↔  Ca²⁺ + 2HCO₃^-                                                         

Equation 1 describes what happens when we boil water with temporary hardness. Calcium carbonate (CaCO₃) is formed and precipitates out of the solution, whilst CO₂ is released.

Equation 2 (a detailed breakdown of what is happening to these compounds) shows that these compounds act as weak bases and raise the water pH (or mash) because hydroxyl ions (OH^-) are produced and CO₂ (which is acidic) leaves the system.

If left uncorrected, the wort will become more alkaline; this can be detrimental as it can cause:

• Poor saccharification
• Poor wort separation
• Dark worts
• Poor biological stability
• Poor protein precipitation
• Astringent beer (polyphenol extraction)

So, why does permanent hardness reduce mash pH? This is mainly because phosphates from the malt interact with the calcium and magnesium ions to release the H⁺ ions and reduce pH. 

The example below illustrates how phosphates interact with calcium ions to release H⁺ ions:

3Ca^₂₊ + 2HPO₄^2- ↔ 2H⁺ + Ca₃(PO₄)₂ ↓

Based on this, we must be able to determine if brewing water is hard or soft, so that we can control the hardness of the water is used in the brewhouse. This will prevent any negative effects on the wort and brewhouse equipment.

Historically, water hardness has been measured in degrees of hardness, but different countries have different definitions. The European Brewery Convention Manual of Good Practice: ‘Water in Brewing’, defines water hardness in the table below:

Table: Degree of water hardness definitions

Note that in Germany, calcium oxide (CaO) rather than calcium carbonate (CaCO₃) is measured. 

The global variations resulted in the need for conversion factors between different countries’ measurements; this caused much confusion. The modern classification of water hardness measures the total hardness as mg/L of CaCO_3.

This is measured by titrating 100 mL of water, buffered with ammonia/ammonium chloride, with the addition of 0.02 M of ethylenediamine-tetra acetic acid (EDTA) to an indicator end point using Eriochrome Black indicator. The EDTA is used to bind and precipitate all of the calcium or magnesium out of the solution. Total hardness is expressed as mg of CaCO₃, where 1 mL of EDTA solution is equivalent to 1 mg of CaCO₃.

To calculate the total hardness of the water using the levels of calcium and magnesium in the water, it is necessary to convert the sum of these to an ‘equivalent’ weight of CaCO₃. To do this, you must convert the ppm (mg/L) levels of the Ca and Mg into equivalents. 

An equivalent is the atomic or molecular weight of an ion divided by the valance of the ion. For example, the equivalent for calcium ions, which have a charge of +2 and an atomic weight of 40, is 20. The atomic weight of Mg is 24.3 and the charge is +2 so the equivalent is 12.1.

We can use two different equations; both achieve the same result:

1. Total Hardness as  

OR

If you take the molar mass (Mm) of CaCO₃ as 100.1g/ml, then the ratio of the molar masses with calcium and magnesium are:

and 

 Therefore, the total hardness as CaCO₃ can be calculated as follows:

2. Total Hardness as CaCO₃ = (2.5 x Ca²⁺) + (4.12 x Mg²⁺)

Let us try to make this clearer by doing an example together: