Note: this discussion assumes a moderate understanding of the importance of pH in the brewing process. If you get lost, please refer to Kai Troester’s excellent discussions on the importance of pH.
Water chemistry–specifically pH, and more specifically, mash pH–is usually the final frontier for a homebrewer, and for good reason: it requires at least a bit of chemistry understanding, it requires an investment to figure out your home water profile (or, alternatively, to purchase distilled or reverse osmosis water continually), it requires some method to calculate or estimate the pH, and lastly, it requires a means to verify the calculated pH value is actually achieved in practice. For the remainder of this post, we’ll discuss only one of these requirements, specifically the method to calculate or estimate mash pH.
While there are a number of mash pH calculators available for free use on the web, until recently, the general consensus is that the most accurate is the Bru’n Water spreadsheet tool, created by Martin Brungard. Empirically, Martin’s tool had always predicted my mash pH with surprising accuracy, which I had assumed was reflected simply by nature of his being the most complex tool, and apparently the most faithful calculation of pH in the mash. Recently, however, Kai Troester has created his own web-based Mash Chemistry and Brewing Water Calculator. Eager to try out a new calculator, I was surprised to find that Kai’s did not produce the same value as Martin’s, even with precisely the same inputs. In a follow-up conversation with Kai, I learned that there is no definitive model for calculating mash pH! This is what Kai had to say:
For a number of pH measurements (experiments and actual brewed batches) I have compared Martin’s spreadsheet and my new water calculator. There are a number of water and grist configuration where BW does poorly with respect to mash pH prediction. Especially when you get into the extremes. But in many cases it does good enough. So I do see that it works for most brewers.
One of the reasons why the models diverge is that the Brewer’s Friend calculator implements the underlying water chemistry more accurately. It actually takes the behavior of the various weak aids into account. Spreadsheets have a problem with that since math that is involved is difficult to implement and debug in a spreadsheet.
Since I learned of Kai’s spreadsheet, I have been using both it and Martin’s spreadsheet to predict my mash pH prior to every brew. In the six batches I’ve brewed since learning of Kai’s pH calculator, Martin’s calculator has been closest for four, while Kai’s closest for two. My brewing process usually involves diluting my high residual-alkalinity tap water with reverse osmosis water to reach the desired pH, and then re-adding the necessary levels of calcium with limited salt additions. Kai’s calculator predicts a mash pH usually 0.2 points higher than the value predicted by Martin’s calculator; it’s been consistent for me, but I’m not sure why.
In the two cases where Kai’s prediction was closest, I had added a relatively high amount of salts and/or acids into the mash (e.g, 4-6 total grams of salts, and 2 milliliters of acid, for a five-gallon batch); and in contrast, in all the cases where Martin’s predictions were closest, the salt additions were low (e.g., 2 total grams, or less), and no acids were added.
TLDR? What is the take-away message? I recommend using both Kai’s and Martin’s spreadsheets for your mash pH estimation. If my experience holds true:
- Use Martin’s spreadsheet to set your target pH and plan your salt & acid additions accordingly;
- Use Kai’s spreadsheet to predict an upper-bound on your mash pH, and prepare supplemental salt and/or acid additions;
- Measure your actual pH in the mash (remember to cool it to room temperature first); and
- If Kai’s pH prediction is closest, use your planned supplemental salt and/or acid additions to reduce your pH into an appropriate range.