Lesson 3 - Brewing Water Sources and Treatment SAQ

**You are looking to build a brewery to produce a black stout on a new site. You have the option of using either surface water or ground water. 

a) Which water source would you use? Explain your decision.

b) You need to treat the water of your choice, in order to make it potable. Provide an overview of the water treatment steps that you would include, up to the point of making it potable. Explain the main function of each step.

Response:

a)    As the brewery is producing a black stout, you should ideally use water with a high residual alkalinity (RA). Surface water is usually low in minerals and hence unlikely to have a high RA. Surface water availability varies from season to season, depending on the rainfall and heat (evaporating water source). Ground water has usually accumulated over many years so its availability should be more reliable. Surface water can also vary in quality, with the potential for high turbidity, colour, agricultural run-off increasing nitrate levels, and high levels of organic compounds and microbes. Mineral levels vary depending on the source, but they are likely to be low.

To get a positive RA, you could select surface water and add in the salts required to boost RA but given the other benefits of ground water it is difficult to justify. Also, it is more difficult to add bicarbonate to water than it is to add sulphate and chloride, because calcium carbonate is insoluble. There is a limit to how much sodium or magnesium (bi)carbonate you can add without ending up with excessive levels of Na⁺ and Mg²⁺ ions in your brewing water.

Due to being filtered through sand and rock, ground water tends to have lower turbidity, colour, nitrates, organic compounds and microbes. Depending on the rock that the water has seeped through, the mineral content could be high, but may contain iron. Since the water has accumulated over years, the quality is unlikely to vary from season to season and you could expect a fairly consistent supply. Based on all these factors, it makes sense to choose ground water as the supply for your brewery.

b) The water would need to be abstracted into a reservoir to ensure a buffer in supply. This storage time also allows sedimentation of larger particles (although this will be minimal due to the ground water source). A small mesh screen may be necessary to trap any solid particles that may have entered the water source or reservoir post-extraction from the ground water source. Water aeration removes the dissolved CO₂ in the water (common in ground water) and oxidises any iron (Fe²⁺) into insoluble ferric hydroxide [Fe(OH)₃], which can then be removed by precipitation or filtration. The water then passes through a granulated, activated carbon filter to adsorb any organic material in the water.

Please note that although there are fewer organics in ground water than in surface water, it is still recommended that you adsorb them to avoid contamination of the ground water supply. The water can then be pH adjusted to meet the required specifications and prevent any corrosion or scaling. Disinfection comes next. You should avoid using chlorine as a disinfectant, as the water will ultimately be treated further down the line, to make it suitable for product water. Chlorine dioxide (ClO₂) would be a preferable choice. However, as an initial disinfectant, chlorine would suffice. Chlorine can form flavour taints in beer (chlorophenol), be toxic to yeast and it can also damage membrane filtration equipment.