Measuring Mash pH

Questions about pH and its relationship to brewing are very deep. So deep in fact, that the pH scale was developed and introduced to the world in 1909 by Søren Peter Lauritz Sørensen, head of the Carlsberg Brewing Laboratory in Copenhagen, Denmark from 1901 to 1938. Maltsters and brewers keep a careful watch on pH because of its influence on all biochemical reactions. Just a shallow scratch of the surface of this topic reveals malt color, enzymatic activity during mashing, color development and hop utilization during wort boiling, trub behavior in the whirlpool, microbial activity in unpitched wort and in fermented beer, and oxidative and colloidal stability of packaged beer, as examples of the myriad aspects of how beer is touched by pH. What follows will not be a rambling journey down this interesting rabbit hole!

Before or After?

I have been spending much more time checking out homebrewing social media since life as we all knew it changed in early 2020. The question about when to adjust pH is perhaps one of the most common questions about this topic. I see my friend and fellow BYO contributor, Denny Conn, frequently posting short quips about this question. The answer is simple; check mash pH after malt is added and the mash is allowed to settle for a bit. A bit? Yeah, more on that in a bit.

Without getting bogged down into the specifics, the pH of brewing water tells a very incomplete story because there are three components in water that have a profound effect on mash pH (calcium, carbonate/bicarbonate, and magnesium), yet only one of the three, carbonate/bicarbonate, affects water pH. And that effect is not simple because carbonate/bicarbonate is a buffer system that opens up a chapter in organic chemistry titled “Buffers, Buffering Capacity, and the Henderson-Hasselbalch Equation.” Suffice to say, water pH is not very useful to brewers because mash pH is affected by stuff in water AND stuff in malt.

When does a brewer measure mash pH? A little bit after mashing in, of course! Proteins, polypeptides, phosphates, and other organic molecules with carboxylic acid moieties react with calcium and magnesium and release protons into the mash; this lowers pH. The carbonate/bicarbonate buffer system is also busy doing its thing, which typically results in mash pH being pushed upwards. Since these reactions do not happen immediately upon mash-in, some time is required for the mash pH to stabilize. Like so many things in brewing, there is no magic time required for pH to stabilize; 15 minutes is usually long enough, but pH usually stabilizes after about 5–10 minutes. In the vernacular of non-specific direction, seasoned brewers say, “wait a bit after mashing in to check mash pH.”

Let’s assume we have mashed in for a nice hoppy, English-style IPA. The recipe is classic: 80% Golden Promise malt, 15% torrefied maize (a.k.a. corn), and 5% medium crystal malt. We wait for 15 minutes, and pull a mash sample. Now what? Well if the brewer is practical, they may have a pH meter with an electrode that doesn’t mind hot measurements and the mash pH is measured. Others will cool the mash to 68 °C (20 °C) before a measurement is taken. So, 15–25 minutes later, we have our pH value. Drats! We discover that our pH is 5.6 and we really wanted pH 5.4. Does the practical brewer add acid? Well, that depends on the practical brewer. This practical brewer would make a note in the brewing log, play with the sample by determining how much acid would be required to adjust the pH, and use this information on the next brew. The problem that many homebrewers have is that the next brew may be an entirely different type of beer.

Target pH is another one of those things that depends on what you are aiming to do. The general rule is to have a pH in the 5.4–5.6 range (measured at 68 °F/20 °C).

Adjusting Mash pH

The three most common methods used to adjust mash pH are through water salt additions, for example, by adding gypsum (calcium sulfate) to your brewing water before the mash, malt selection, and acid additions. Your question was thankfully simple in that you asked for the methods, not a deep dive into the chemistry behind the method. Basic calculations are, however, required to estimate mash pH. Here is a method for estimating mash pH:

Estimated Mash pH = (wort pH from malt COA) + (RA x 0.03) – (% crystal malt x 0.025) – (% lightly roasted malts x 0.03) – (% darkly roasted malts x 0.05) – (% acidulated malt x 0.01).

Residual Alkalinity (RA) = (ppm carbonate/bicarbonate in water x 0.046) – (ppm calcium in water x 0.04) – (ppm magnesium in water x 0.03).

And here is an example:
Assume the grist bill is 95% base malt and 5% crystal malt (note this method does not have a spot for adjunct grains), and the water contains 60 ppm carbonate/bicarbonate, 120 ppm calcium, and 20 ppm magnesium. You need to check a “COA” (certificate of analysis) of the base malt used for this brew. That information is not always easy to find, but for this malt let’s assume we know that the value is pH 5.9 at 68 °F (20 °C).

RA = (60 x 0.046) – (120 x 0.04) – (20 x 0.033) = -2.70

Estimated Mash pH = (5.9) + (-2.70 x 0.03) – (5 x 0.025) = 5.7 at 68 °F/20 °C

In the example above, the predicted mash pH is higher than the target. The options for mash pH adjustment are water chemistry, tweaking the grist bill, and adding acid. The equations above show the basics on using water and malt selection to adjust pH. What about adding acids? Definitely an effective, relatively easy, and common method, with lactic and phosphoric acids the most common food-grade acids used by brewers.

The general rules for these acids are that 0.66 grams of either 88% lactic acid or 85% phosphoric acid added to 1 kg (2.2 lbs.) of grist (“normal” mash thickness in the 3 liters water per kg malt is assumed) will reduce mash pH by 0.1 pH units. For my non-metric friends, this translates to 0.01 ounces of acid per pound of malt in a normal mash with a thickness of 1.4 quarts per pound.

Beer Stability, pH, and Dry Hopping

A topic that is likely to receive more attention in the near future is the relationship between beer pH and dry hopping. In general terms, dry hopping increases beer pH. Practical brewers and brewing scientists have noted that the very high dry hopping rates used for hazy IPAs have resulted in more packaged beers with pH > 5.0. Beer pH is usually in the 4.2–4.8 range and when beer pH gets into the 5s, oxidative and microbiological stability both take a dive. One technique that is really gaining some traction is wort pH adjustment after the boil to reduce pH going into fermentation to about pH 4.8. Brewers are also using post-fermentation acid additions to lower in-package beer pH to specifically address oxidative stability. Thanks for the great question about pH. Hope this information is useful in your quest for great beer!

Response by Ashton Lewis.