Hardness and alkalinity Part 1

Water hardness and alkalinity are some of the trickier aspects of brewing to get a grip of but the benefits and improvements it can bring to your brewing make it well worth looking into. Suitable water improves every step of the brewing process. I already outlined the importance of calcium in a previous post. This post is a guide to assessing the hardness of your water supply and its suitability for mashing. First we need to get some definitions straight as it is these phrases that often cause the most confusion:

Hardness: This is essentially the concentration of calcium and magnesium in the water. It is divided into two further sets of terms:

Permanent hardness also called non-carbonate hardness. This cannot be removed from the water by simple means. It is made up from calcium and magnesium compounds such as calcium sulphate, magnesium sulphate, calcium chloride and magnesium chloride.

Temporary hardness also called carbonate hardness or alkalinity. This can be removed through the various treatments that brewers use, and is responsible for the lime-scale on household appliances. It is made up of calcium carbonate and calcium bicarbonate.

The significance of the distinction is seen when we consider what the two types of hardness bring to brewing. Carbonate hardness increases mash pH by neutralising the natural acids contributed by the mash, dragging the mash pH away and above the 5.4 that is optimal for malt amylases to work. Non carbonate hardness lowers mash pH and is beneficial to meeting the optimal mash pH.

The contrasting action of these differing forms of hardness leads us to another important term in brewing water chemistry: residual alkalinity. This is the net effect of the water hardness on the mash, and the extent to which the water will have to be treated to meet requirements. For most Irish water supplies carbonate hardness will out-weigh non carbonate hardness and the water will require a degree of treatment to lower the alkalinity.

Water reports state water hardness in 'equivalents' of calcium carbonate or bicarbonate. This is necessary in order to compare the different types of hardness in the water on a equal footing. When compared in this way it is seen that 3.5 equivalents of permanent calcium hardness or 7.5 equivalents of magnesium hardness is required to offset the pH raising effects of 1 equivalent of carbonate hardness. It is clear from these figures that carbonate hardness is very potent at increasing mash pH. If your water supply is low in carbonate hardness it might be possible to offset the residual alkalinity through the addition of calcium sulphate or calcium chloride, which is likely to be added at any rate in order to increase the calcium concentration to a more suitable level. However, if the carbonate hardness is very high, adding calcium to the water will not be sufficient to overcome the residual alkalinity and the carbonate hardness must be removed.

In my next post I will provide some simple methods for estimating alkalinity, and how to remove it.