Mash pH – Hard Water Treatment for Brewing Beer

by Brad Smith on October 5, 2008 · 33 comments

For many years I never worried about balancing pH or even what my water profile was when brewing. After all, the beer was fine and most of the time I was brewing with extract, so pH did not matter much.

However once I started all grain brewing, the water I brewed with suddenly started to matter. It also helped that I moved to an area with extremely hard water, which forced me to use bottled water to produce anything reasonably resembling beer. It turns out that the pH of your mash has a huge impact on the mashing process as well as taste of your finished all-grain beer.

Understanding pH: Alkalinity and Acidity

Pure water has a pH of 7.0, which means that it is neither acidic nor alkaline. If you are into chemistry, this means that the free H+ (hydronium) ions are balanced with the OH- (hydroxide) ions giving equal concentrations capable of forming H2O. If water has an excess of H+ ions, we call it acidic (lower pH), while an excess of OH- ions gives us alkaline (higher pH) water.

Now it we take our pure water in the form of rain and run it down through the atmosphere and soil it picks up CO2 and Calcium from the soil, these elements will bind with the H+ ions leaving a bunch of free OH- (hydroxide) ions making our water more alkaline. This increases the pH of the water. Most tap water is slightly alkaline for this reason. Really hard water can be highly alkaline.

Interestingly all malts (and dark malts in particular) have phosphates in them that react with the calcium and magnesium ions in alkaline water freeing up H+ ions that make the mixture acidic. Adding malt, especially dark malt, lowers the pH of the malt water mixture in the mash.

The Importance of Mash pH

The pH of the mash is very important for proper conversion of sugars during the mash and also due to its effect on finished beer. Mashing should always take place at a pH between 5.1 and 5.3. However, its important to note that we are talking about the pH of the mixed mash, which as I point out above depends on the color and quantity of malts added to the beer. In most cases the mixed mash will be slightly alkaline (pH above 5.3) and require an acidic addition or buffer to bring it down to 5.2.

Though some commercial brewers can accurately predict the pH of their mash in advance, few homebrewers have the detailed knowledge and data available to do this. The problem is that the color, quantity and even type and supplier of the malt can change the pH. In addition, your starting water and its interactions with the malts may vary with each recipe. Remember that commercial brewers brew the same recipe every time using the same ingredients, while homebrewers do this only rarely.

That’s why homebrewers are reduced to measuring the pH of each mash right after it is mixed and then adjusting our pH as early as possible in the mashing process.

Measuring pH can be done in several ways including pH (litmus) strips, precison pH strips and even using an electronic pH meter. Of the three methods, precision pH strips are usually most cost effective and practical. Standard pH strips lack the precision needed to measure down to a tenth of a point pH, and electronic meters are expensive and require frequent replacement of the electrodes to maintain accuracy.

Another practical consideration is that the mash is usually hot, so you need to adjust the pH reading for temperature. Hot wort will almost always provide a higher pH reading than the actual wort. You can compensate for this either by rapidly cooling the sample to room temperature before measuring or applying a correction factor after taking the reading. Check the documentation with your pH strips to determine the appropriate correction.

Methods for Adjusting Mash pH

There are several methods available to the homebrewer for adjusting the pH of your wort. As noted earlier, in most cases you will need to lower your pH to reach the 5.2 target level.

  • Calcium and Magnesium Salts: Three salt: Gypsum (CaSO4), Epsom Salt (MgSO4) and Calcium Chloride (CaCl) can be added to lower your pH. The calcium and magnesium ions in these additions reduce the alkalinity of the water. Note, however, that the sulfate and chloride ions react with the phosphates from the mash, which can lead to undesirable flavors. As a result you need to limit the amount added. You can calculate appropriate amounts using a water tool such as the one in BeerSmith. Suggested limits are 50-150 ppm for calcium, 50-150 ppm for sulfate, 0-150 ppm for chloride and 10-30 ppm for magnesium. See our article on water profiles for more information.
  • Food Grade Acids - Acid additions counter the H+ ion and directly lower the alkalinity of the mash. Popular additions include phosphoric acid, sulfuric acid and lactic acid. All of these contribute other flavors and ions to the beer as well, which can again cause problems if used in excessive amounts. Phosphoric acid is used to make soda, and will contribute phosphates to the mash. Lactic acid will add lactates, and is used in many Belgian styles to sour the beer. Sulfuric acid will contribute sulfates. In general you should add the minimum needed to achieve your target pH. The amount will vary depending on the concentration of your acid and wort volume.
  • Acid Malt – Because of German purity laws (the Reinheitsgebot) that prevent additives to German beer, sour malt (called acid malt) is used to aid in the brewing of light beers to lower mash pH. Acid malt is made by souring malt with lactic bacteria for a short period which effectively creates lactic acid. Adding acid malt is effectively equivalent to adding lactic acid to the mash. Adding one percent of acid malt effectively lowers the pH of the malt by approximately 0.1 pH.
  • Sour Mash - Another technique developed by the Germans is to create a sour mash which again contains lactic acid produced by lactic bacteria. The technique is to mash a quantity of grain, cools it to about 80F and then adds some fresh malt (which contains lots of lactic bacteria naturally) and lets the mixture sit overnight. The bacteria will quickly sour the mash and start fermenting it, again creating lactic acid. The next day this sour mash can be mixed with a regular mash to lower its pH. The challenge with sour mashing is that it can be somewhat inconsistent in pH and also labor intensive.
  • Acid Rest - Though seldom used today thanks to modern highly modified malts, an acid rest in the 95F (35C) range can break down phytins in the malt into phytic acid that will lower the mash pH. This was traditionally done in German triple decoction mashes, and is most effective when used with undermodified malts.
  • 5.2 Stabilizer – A number of brew stores now carry an additive called 5.2 stabilizer. This is a powder you can add to the beer to lower the mash pH to 5.2. It consists of buffers that reduce the alkalinity of the mash to reach a 5.2 level. As long as your starting water is not completely out of kilter, this is a good simple solution for many homebrewers.

I hope you enjoyed this week’s article on mash pH. Please join us next week on the BeerSmith Home Brewing Blog for another great article or subscribe for regular delivery.

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