Lesson 8 - Water Final SAQ

***Water hardness is a key property of brewing product water. Explain what water hardness is, its impact on the brewing process and how it can be controlled.

Response:

Water hardness is determined by the water’s mineral content. Hard water means that the water has a high mineral content, mainly made up of the salts of calcium and magnesium ions, with bicarbonate, carbonate, sulphate, chloride or nitrate ions. Soft water means that the levels of the same minerals in the water are low.

The ‘hardness’ of a water source can be tested quickly by using soap in the water. Hard water collapses soap lather as it forms insoluble salts of fatty acids, which then precipitate. So, 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’.

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

Total hardness = Permanent hardness + Temporary hardness

The key difference between the two is that temporary hardness can be removed by boiling the water, whereas permanent hardness cannot.

Water with high levels of hardness can cause scaling, which will negatively affect the heating surfaces’ performance, such as with the wort kettle. This will lead to reduced wort boiling efficiencies, which can ultimately lead to out of specification worts. This includes off-flavours and low hop utilisation. It may also require an extended boil time, to achieve the correct evaporation rate so that we meet the original gravity specification.

Temporary hardness can also cause an increase in mash and wort pH:

(Equation 1)

(Equation 2)      

Calcium carbonate is formed during boiling. It precipitates out of the solution whilst carbon dioxide is released. However, as can be seen in equation 2, the bicarbonate ions can lead to the release of hydroxyl ions. These act as a weak base and raise the pH of the wort during wort boiling or mashing. If left uncorrected, the mash or wort will become alkaline. Unfortunately, this could cause:

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

With permanent hardness, the sulphates, chlorides and nitrate ions are acidic and thus reduce the pH of the water. 

Many substances such as phosphates, organic acids, phytates and proteins are extracted from the malt. They interact with the calcium and magnesium salts to release the hydrogen ions to reduce pH.

The example below illustrates how phosphate complexes interact with calcium ions to release hydrogen ions.

Water hardness can be controlled in a number of ways.

Temporary hardness can be removed by the following methods:

• Heating – As described previously.
• Treatment with lime ‒ Calcium hydroxide and bicarbonate react to form lime scale (calcium carbonate), which precipitates out and settles to the bottom of the vessel.

• Treatment with an acid ‒ Inorganic or organic acid is added to the water, which reacts with the bicarbonate to release carbon dioxide and form calcium.

• Ion exchange – WAC, SAC, WBA and SBA all exchange ions for hardness ions.
• Reverse Osmosis – Removes all ions from the water.

Permanent hardness can be removed by:

• Ion exchange – SAC, WBA and SBA (not WAC) all exchange ions for hardness ions.
• Reverse osmosis – Removes all ions from the water.