Ask Mr. Wizard

Predicting Mash pH


Dennis Sopcich — Loves Park, Illinois asks,

I have been an all-grain homebrewer for almost 15 years now. I typically start with reverse osmosis (RO) water and add Ca+2, Mg+2, Na+, HCO3- and Cl- as needed, depending on the beer that I am brewing. I measure mash pH and am normally within the recommended range of 5.2 to 5.5. What I would like help with is a formula for calculating/estimating mash pH so that I can make appropriate pre-mash acid/base adjustments vs. trying to catch up after the fact. I have used the Braukaiser spreadsheet but would like to see a summary of the actual formulas and supporting data used/needed to make reasonable pre-mash pH estimates. I am an engineer by training, so I’ll gladly labor through the math. 


Being able to predict mash pH based on brewing water composition and grist bill is something of great practical use to brewers. Clearly not all beer styles brewed in Munich, for example, are a good fit with the alkaline water in Munich without some adjustments and having some way to guide these tweaks before a brew is the general aim of many water calculations. The fact is that all such calculations are approximate because there are simply too many variables that affect mash pH, including water, malt, mash profile, boiling duration for decoction mashing, and mash thickness. I have spent a fair amount of time digging into your question and can provide some answers, so read on!

The most recent version of Kai Troester’s water calculator I could find on the Braukaiser website is version V1.58 dated September 16, 2012. The bad news is that this spreadsheet is password protected and the formulas are hidden. That’s probably why you submitted this question. The good news is that I am persistent with Excel and was able to find a tool to remove the password! Sorry Kai, but I had to pick your lock.

Let’s start with a summary of how Kai’s water spreadsheet is written. This tool is based on the work of Paul Kolbach that was first published in 1951. The translated title of his work is “The Influence of Brewing Water on the pH of Wort and Beer.” A.J. Delange translated pieces of this work collected by John Palmer and some of the German text was cleaned up by Kai Troester for translation. The translated document is not dated, but can be found at Kolbach developed the brewing concept of residual alkalinity (RA), expressed in terms of equivalents of calcium oxide, and came up with an easy-to-use factor equating +/- 10 units of RA to +/- 0.3 pH units. Let’s assume we produce wort using distilled water for mashing and sparging and our post-boil wort has a pH of 5.6. If we repeat the same brew with water with RA = +10, the predicted post-boil wort pH is 5.9. The same logic can be applied to mash pH estimation.

In Troester’s tool, he begins by calculating RA and applies a correction factor for mash thickness to account for the differences between predicted wort pH and mash pH (see for a review of how to calculate RA). Troester references his excellent white paper titled “The Effect of Brewing Water and Grist Composition on the pH of the Mash” published on his Braukaiser website where he provides extensive data related to the general topic, including specifics about mash thickness, mash pH, and how these relate to Kolbach’s wort pH rule. The takeaway here is that RA = +/- 10 °dH (degrees of German hardness) equates to a +/- 0.2 mash pH change when mash thickness is 4 parts water to 1 part malt (wt/wt). That’s a bit on thin side for most homebrewing (3:1 is more common), but as the data in Table 1 shows, mash thickness only has a minor effect on predicted mash pH.

Troester’s tool also calculates the predicted pH of mash using distilled water where RA = 0. This is where things become a little odd. Because distilled water has no RA, mash thickness does not affect predicted mash pH and the value that is returned is based solely on color and a big assumption about all pale malts. When color is set to 2 SRM, the predicted pH of mash produced from distilled water is 5.57. Not only does the pH of mashes made from different pale malts vary quite a bit, but it’s usually higher than 5.57. Most North American pale malts these days have a reported pH based on ASBC (American Society of Brewing Chemists) congress mashing of around 5.9. The easy way to use this information is to increase his estimates based on known values obtained from current malt analyses. You can see from the data in Table 1 that the predicted pH changes based on wort color and mash thickness are linear over the range shown, so the adjustment can also be linear.

Troester’s 2009 white paper takes a deep and very interesting dive into the topic of color, but incorporating the results of his mash trials into a single calculation is not simple because pale malts, crystal malts, high-kilned, and roasted malts all affect mash pH differently. In his Braukaiser calculator, he uses a single term combining beer color, % roasted malt, and % non-roasted malt as the way to bring specialty malts into his prediction of mash pH. Note that on a beer color basis, non-roasted malts, assumed to be crystal malts used in his pH shift calculation, are more acidic than roasted malt. This term is calculated by the following:

pH Shift from Color = (-) {(Beer Color in SRM) x [(0.21 x % non-roasted malt) + (0.06 x % roasted malt)]}/12 °Plato.

Although the Braukaiser pH shift from color term appears to be based on solid data, it seems to overestimate the effect of malt color on mash pH. Table 2 shows predicted mash pH at a single mash thickness using alkaline water (RA = 10 °dH) over a range of colors and their corresponding roasted malt component. Troester’s plots of mash pH versus beer color in his white paper don’t fall below about 5.1 when color is derived from roasted malt, yet the predicted mash pH from the combination of 10% roasted malt and 90 SRM is 4.35.

What does this all mean? In my opinion as someone who has written lots of spreadsheets, any review of a spreadsheet is likely to find some oddities. I noted a few because you asked how this tool is written. It’s also my opinion that Kai Troester developed a user-friendly, predictive tool to help navigate the deep topic of water chemistry. If I were to edit this tool, I would “unbury” the pH from base malt and make that an editable variable. I would also spend more time looking at the pH shift from color because it doesn’t pass the sniff test; other references coupled with my own brewing experience are not aligned with that metric.

It’s weird; every time I remove a liter from the brewing water well, it has more water when I return! This review is a good reminder that these types of tools are predictive and are never perfect. Users must be prepared to take notes and adjust their subsequent brews based on the results of the present. That’s my view on the meaning of this exploration.

And back to you, Dennis. Engineers like to understand their tools. Your question sent me on a fun quest that included watching numerous YouTube videos on how to unprotect Excel sheets when you don’t have the password, reading multiple articles about water, and digging into a complex spreadsheet. If you want to learn more, start with figuring out how to sneak past the lock!

Response by Ashton Lewis.