by Ginger Wotring, revised in 2017 by Scott Bickham

Water constitutes 85‑95% of beer, with the remainder being compounds derived from malt, hops, and yeast. As a general rule, if tap water is drinkable, it may be used in brewing, although some mineral adjustments may be needed to mimic the water used in some historical beer styles. Most tap water is also treated with chlorine to inhibit bacterial growth, and this should be removed to produce high-quality beer.  Note that the processes used to make reverse osmosis (RO) and distilled water strips out trace minerals such as iron, manganese, copper, and zinc, which are essential for yeast metabolism, so mineral water is often a better choice.  Finally, most water contains very low concentrations of bacteria, so it must be sterilized by boiling at some point in the brewing process.

Alkalinity, pH and Hardness

Water is a solution of ions with negative (anions) and positive (cations) charges. The water molecules (H2O) themselves are also partially dissociated into hydroxide (OH) and hydrogen (H+) ions, and the pH, a chemical shorthand term referring to the concentration of hydrogen ions, indicates the relative concentrations of these ions. Neutral water has equal OH and H+ concentrations corresponding to a pH of exactly 7. Lower pH values indicate a higher H+ concentration and acidic water, while higher pH values correspond to a higher OH concentration and thus alkaline water. In brewing, the pH is determined by the hardness, alkalinity and buffering salts derived from the ingredients.

Alkalinity is a measure of the capacity of the dissolved anions to neutralize reductions in the pH value of the solution. The most important anion at the pH of brewing water and wort is bicarbonate (HCO3), because HCO3 is the primary ion that determines the alkalinity of water. Bicarbonate reacts with Calcium (Ca+2) ions when boiled to form a calcium carbonate precipitate and water:

Ca+2 + 2HCO3 = CaCO3 (ppt) + H2O + CO2 (gas)

Boiling drives off CO2, thus forcing Calcium and HCO3 ions from solution and reducing the alkalinity. Permanent hardness is a measure of the cations that remain after boiling and racking the water from the precipitate, and is primarily due to Ca+2 and Magnesium (Mg+2) ions. These cations are permanent if they are derived from sulfate or chloride salts and temporary if they originate in carbonate or bicarbonate salts.

When a grist consisting of 100% Pils malt is mashed using distilled water, which has a pH of 7.0, the mash pH typically ends up between 5.7 and 5.8.  This pH reduction is due to the enzymatic degradation of phytin in the malt to form phytic acid and calcium or magnesium phosphates, which precipitate. Most of the phytic acid combines with free Ca+2 to form more calcium phosphate, releasing hydrogen ions in the process.  Most brewing water has enough calcium or magnesium for this process to regulate the mash pH to the target 5.1-5.5 range, which is appropriate for the breakdown of starches and proteins.

Some water supplies have too much alkalinity for this process to be effective, in which case the mash pH can be reduced to the proper level by adding lactic or phosphoric acid to the brewing liquor when brewing pale-colored beers.  Another method of adjusting the mash pH is through the addition of acidulated malt, which is produced by using lactic acid generated by the naturally occurring lactobacillus on the grain.  When using toasted, caramel and roasted malts to brew amber and darker-colored beers, the natural acidity of the malts can have a significant effect on the pH.  For example, using a dark crystal or roasted malt for 20% of the grainbill can reduce the pH by 0.5, which is usually sufficient to bring it to the proper level for starch conversion.  The need to include malts kilned at higher temperatures in the grist played a role in the development of several historical beer styles, as will be discussed below.

Ions in Brewing

The most important cation in brewing is calcium, which is essential for reducing the mash pH to the appropriate range.  It also helps keep oxalate salts in solution (they form haze and gushing if they precipitate), reduces the extraction of tannins, and assists in protein coagulation in the hot and cold breaks. Magnesium ions participate in the same reactions, but are not as effective. Yeasts require 10-20 ppm Mg as a nutrient, but higher amounts give a harsh, mineral-like taste. Another cation is sodium, which accents the sweetness of beer at low levels, but tastes salty at higher concentrations.  This salty-sweet character is part of the flavor profile of the Gose style.

The most important anion in brewing is bicarbonate (HCO3), because it determines the alkalinity of the brewing water. Bicarbonate neutralizes acids from dark and roasted malts, reacts with calcium to reduce the hardness and promotes the extraction of tannins and coloring compounds. It is normally in solution with small amounts of carbonate (CO3-2) ions, but the bicarbonate is by far the most important component at typical pH values of water and wort. The sulfate (SO4-2) ion does not play a significant role in the brewing process, but accents hop bitterness and dryness at the high concentrations found in the waters at Burton-on-Trent. Another anion is chloride (Cl), which enhances sweetness at low concentrations, but high levels can hamper yeast flocculation.

Famous Brewing Waters

The ions described above are found in different concentrations depending on the source of the water, as shown in the table below for several major brewing centers (data is in ppm and taken from John Palmer’s How to Brew):

Mineral Calcium Magnesium Sodium Sulfate Bicarbonate Chloride
Plzen 10 3 3 4 3 4
Dortmund 225 40 60 120 220 60
Munich 109 21 2 79 171 36
Vienna 163 68 8 216 243 39
Burton 352 24 44 820 320 16
Dublin 118 4 12 54 319 19
Edinburgh 100 18 20 105 160 45
London 52 32 86 32 104 34

These water compositions have played an important role in the development of world beer styles. How to Brew provides a good linkage between the mineral content of these waters and historical beer styles that is summarized below:

Pilzn – The very low hardness and alkalinity allow the proper mash pH to be reached with only base malts.  These characteristics, combined with the lack of sulfate, yields the rounded malt character and mellow hop bitterness of the Czech Premium Pale Lager style.

Dortmund – The higher level of all minerals in this city and other regions of Northern Germany enables brewers of the Dortmunder Export and German Pils styles to produce pale lagers that are bolder, drier, and lighter in color than their counterparts from the Czech Republic.

Munich and Edinburgh – The mineral profiles of the waters of these cities are remarkably similar.
The darker malts used to brew amber and dark German lagers and Scottish ales balance the carbonates and acidify the mash, yielding a very smooth malt character. The relatively low sulfate content also provides a mellow hop bitterness.

Vienna – The level of calcium in the water of this city is too low to balance the bicarbonate level to achieve a sufficiently low pH when brewing pale colored lagers.  However by kilning malt at higher temperatures, the malt developed more color and acidity, and this led to the birth of the reddish-amber colored Vienna lager style.

Dublin – The water from this city has an ever greater imbalance of calcium and bicarbonate than Vienna, and this led to creation of the Irish Stout style, which is brewed using a high percentage of roasted barley and malts.  This style has a relatively high IBU level, but the finish is softened by the low levels of sodium, chloride and sulfate in the water.

London – The bicarbonate level of London water is nearly twice that of calcium, and brewers were forced to use a higher percentage of dark malts to balance the mash pH.   The high sodium content and low sulfate content of the water help smooth out the flavor profile of brown British beers such as Dark Mild and English Porter.

Burton-on-Trent – The calcium and sulfate are both much higher than for any other city listed in the table above, but the calcium is nearly perfectly balanced by the bicarbonate.  This enabled brewers to produce British Bitters which were lighter in color than the ales brewed in London.  The high level of sulfate and low level of sodium produce an assertive, clean hop bitterness.

Water Adjustment

The waters at these brewing centers may be reproduced by adding various salts to locally available water. For additions meant to improve the buffering capacity of the mash, the volume of the water should be used. For salt additions to change the flavor profile of the finished beer, the target volume of the beer should be used. The most common salt additions are gypsum (CaSO4.2H2O — CaSO4 hydrated with two water molecules), Epsom salts (MgSO4.7H2O), non-iodized table salt (NaCl), calcium carbonate (CaCO3) and calcium chloride (CaCl2.H2O). The addition of gypsum and Epsom salts is known as Burtonizing, since it elevates the hardness and sulfate concentrations to levels similar to that found at Burton-on-Trent. Other salts may be used, but these are by far the most common additives in brewing.

Further Reading

  • Dave Miller, Dave Miller’s Homebrewing Guide (Garden Way Publishing, Pownal, VT 1996).
  • Gregory J. Noonan, New Brewing Lager Beer (Brewers Publications, Boulder, CO, 1996).
  • George Fix, Principles of Brewing Science (Brewers Publications, Boulder, CO, 1989).
  • John Palmer, How to Brew (originally published in 2006).