Bicarbonate

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Bicarbonate ion (HCO₃^–) is often present in tap water in fairly high levels. The bicarbonate is responsible for the alkalinity of water because it reacts with acid (H⁺) to form neutral products. Effectively, any bicarbonate in the brewing water directly increases mash pH (and sparging pH, if applicable), which carries forward to affect the boil pH, fermentation pH, and beer pH as well. Alkalinity is arguably the most important parameter of the brewing water due to the huge role that pH plays in the brewing process and the tremendous effect it has on beer quality. In order to avoid an excessively high pH during mashing (and sparging), it is often necessary for brewers to neutralize excess alkalinity either by adding a mineral acid (e.g. lactic acid), or by other methods (see brewing pH). The levels of calcium and magnesium in the brewing water also counteract the pH effects of the bicarbonate.

There is no bicarbonate ion present in beer because bicarbonate is a base, and beer is acidic. During the brewing process the bicarbonate is removed either by reacting with acid to form carbon dioxide and water, or by combining with a cation such as calcium to form an insoluble product that is removed.

Potential sources of bicarbonate

Typically the bicarbonate comes solely from the brewing water, although in styles where increasing the pH is needed, it can be added with a brewing salt.

• Brewing water -
• Salt additives - Sodium bicarbonate can be used to add bicarbonate to the water if it is needed to increase pH. Calcium carbonate should not be used for this purpose because it is poorly soluble.

Total alkalinity is defined as the amount of strong acid (mEq/L) required to neutralize all the carbonate and bicarbonate in the sample (to pH 4.3 or 4.5). This is then converted to "total alkalinity as ppm CaCO₃".

Bicarbonates are especially problematic for more pale beer styles, as they increase the mash pH. The reason is the formation of carbonic acid (H2CO3) from the bicarbonate and the subsequent removal from the mash as CO2 owing to heating. During this process, bicarbonate acquires H+ ions, which leads to the pH increase previously discussed. As a consequence, the ideal brew water contains only small quantities of total alkalinity. However, for darker colored beers there is a need for higher alkalinity to achieve proper mash pH.

When water containing both calcium and bicarbonate is heated, these ions react to form calcium carbonate, which precipitates as scale.

The formula for residual alkalinity (RA) from Kolbach balances the contradicting effects (pH decrease by calcium and magnesium, pH increase by bicarbonates), allowing one to predict the influence of the brew water on the mash pH.

In 1953, Paul Kolbach determined that calcium and phosphate react with malt phosphates to neutralize water alkalinity and reduce the wort pH. Any alkalinity remaining after this reaction is called "residual alkalinity".

Bicarbonate increases the pH of water as it absorbs acidity. Nearly all water contains a certain natural level of bound CO 2 and bicarbonate. Bicarbonate buffers any acidity, for example that caused by CO 2 or other acids like lactic or phosphoric acid. Before the artificial acid can bring down the pH, the bicarbonate has to be destroyed first. Bicarbonate, though, can also be responsible for formation of a layer of lime on mild steel piping which protects the piping from corrosion. This is of less importance nowadays, though, as stainless steel is the preferred material in today's brewery environment. It also should be noted that when water comes into contact with mild steel in the form of pipelines, reservoirs or vessels, free aggressive CO2 has to be removed beforehand by a CO 2 -trickler and the so-called +p (phenolphthalein) alkalinity (pH > 8.2) has to be adjusted.

See also

• Water
• Brewing pH