by Dave Miller (Brewing Techniques)
Question: After seeing references in various beer publications and books on water analysis, I decided to contact my local officials and get a copy of the breakdown for our local water supply. The contents of the report indicate that carbonates are <1 ppm and that bicarbonates are 160 ppm. My reference material discusses carbonates but not bicarbonates. Should I treat carbonates and bicarbonates as the same thing?
One person told me that the amount of bicarbonates in water is related to temporary hardness. If this is so, in comparing my water supply to other water supplies in various parts of the world, do I look at the initial hardness of my water, or the hardness of my water after it has been boiled? Is it true that adding chalk to water raises temporary hardness? If so, does it matter when I add chalk to the boil? If it’s going to precipitate out, why add it at all?
One last question: When I use my copper wort chiller the liquid changes the copper coils from a dull color to a bright finish. Is my wort too acidic?
Dave Miller: In a sense, carbonates and bicarbonates are the same; in another sense, they are not. They are the same because they freely change from one to the other, depending on the pH of the water in which they are found. In low-pH water, such as yours, carbonate ions are scarce. Raise the pH of that water, and some of the bicarbonate ions would become carbonate ions.
Carbonate and bicarbonate differ, however, in that bicarbonates are considerably more soluble than carbonates. Calcium carbonate (chalk), for example, is only slightly soluble in neutral (pH 7) water; calcium bicarbonate is considerably more soluble.
Now let’s talk about hardness. Hardness, strictly speaking, refers to a water sample’s content of calcium and magnesium ions. (For the rest of this discussion, I refer only to calcium, just to keep things simple. In general, magnesium resembles calcium in its behavior, except that magnesium salts, including magnesium carbonate, are somewhat more soluble in water than are calcium salts.) Permanent hardness is hardness that cannot be removed by boiling the water. Temporary hardness is hardness that can be removed by boiling. In temporary hardness, most of the hardness is attributable to calcium bicarbonate. Boiling such water causes the bicarbonate ion to become a carbonate ion, which then binds with calcium. Calcium carbonate is almost insoluble, so it precipitates, thus removing both calcium and carbonate from the water. Because carbonate is alkaline in character, the alkalinity of the water decreases at the same time.
In effect, boiling water like yours will reduce the carbonate/bicarbonate (“total alkalinity”) from 160 ppm to 30–40 ppm. This is very significant because it will enable you to brew pale beers. As is, your water is best suited for making very dark beers, such as stouts and porters, which use a large amount of dark, acidic malt.
In comparing your water to other water supplies in the great brewing cities of the world, you should probably compare the initial carbonate/bicarbonate content. Traditionally, brewers did not preboil their water. However, you can also estimate the hardness (calcium content) and alkalinity (carbonate/bicarbonate content) of your postboil water and compare those figures with various brewing waters of the world. For estimation purposes, figure that for every 5 ppm of carbonate you remove you also remove 3 ppm of calcium. In your case, assuming you aerate the water thoroughly before boiling, you can precipitate ~125 ppm of bicarbonate, leaving ~35 ppm in the water. At the same time you would reduce the calcium content by about 80 ppm.
Though you can do the comparisons, it is best not to get too devoted to the idea of duplicating the water of a particular brewing center. It may not be possible, especially in the case of very soft water like that of Pilsen — at least, not without distillers or deionization filters. Also, it is unnecessary and may not even be desirable. To continue with the Pilsen example, if you duplicate Pilsen water, you will also have to duplicate the Pilsener brewing method, which is a triple-decoction mash that takes 5 h to complete. The decoction mash is necessary to lower the pH of the mash and to get a good conversion reaction. If you tried to use an infusion mash with this water supply, the mash pH would be too high. It is perfectly possible to brew Pilseners with the infusion method, but you must have a calcium content of 50-100 ppm combined with very low total alkalinity (<75 ppm). In other words, your soft water would work, but you would have to add calcium chloride or calcium sulfate to the mash.
Adding chalk to water does not increase temporary hardness, for the reason already given: calcium carbonate is almost insoluble in neutral or alkaline water. There is no reason to add it to the water before boiling. If you need to add carbonate to raise the pH of the mash, you must put it directly into the mash. A dark malt mash is more acidic than a pale malt mash, and carbonate will dissolve in the mash and raise its pH. This treatment, however, is needed only when using water of very low alkalinity and low pH.
To answer your question about the wort chiller, the mildly acidic wort dissolves the surface layer of corrosion on the copper coils. This reaction is normal and does not mean your wort is too acidic. The same thing happened to me and I checked my wort with a pH meter. It was fine.
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