I'm pleased to announce that I finally finished my paper on “The effect of brewing water and grist composition on the pH of the mash”. To this point, this is my most detailed work and it represents data collected in experiments that I conducted during most of this year:
It all started with this discovery and blog post: http://braukaiser.com/lifetype2/inde...d=128&blogId=1
When I was writing a water spreadsheet, I noticed that chalk is not correctly considered for its alkalinity contribution in most of the water spread sheets that existed out there. 100 ppm CaCO3 is assumed to add only 50 ppm alkalinity as CaCO3. This didn't make sense to me and before I was going to tell others about this I thought I better run a few experiments to see what the actual alkalinity contributed by chalk would be. I ended up noticing an oddity in the mash pH resulting from water with undissolved and water with dissolved chalk that led me to do further investigation. But I didn't feel like stopping there and expanded the experiments to include the effects of various malts, calcium, magnesium, mash thickness and milling. The result is aforementioned paper.
But that paper is not intend to tell brewers how to build their water and calculate mash pH. At least not in understandable language. It makes a lot of assumptions of prior knowledge and unless you already have a good understanding of water chemistry in brewing it may not be of much practical use for you. In the following months I plan to write more practical and easier to understand articles which will be based on my findings during the experiments. I also want to update my water spreadsheet to include that data to allow for the estimation of the mash pH to a reasonable accuracy. Stay tuned for that.
Here are the new things that I found out.
- The darker the lower the mash pH applies to most of the malts but there are a fair number of exceptions and the color → mash pH correlation is rather loose
- cara type and base malts provide more acidity per unit of color than roasted malts. This is in direct contradiction to current knowledge but supported by titration and mash pH experiments.
- Kolbach's work on pH in brewing has been misinterpreted to some extend. He was talking about the pH of the cast out wort while we are talking about the pH of the mash. I to didn't notice that until I reviewed his work more closely. In particular the pH change per ppm of CaCO3 residual alkalinity change is not 0.0017 pH but depends mainly on mash thickness. The thicker the mash the lower this number is (i.e. the less the pH changes with residual alkalinity changes)
- the concept of residual alkalinity is a valid one but the neutralizing power of calcium and magnesium are not necessarily constant.
- Chalk not dissolved by CO2 does a very poor job of raising pH. In particular above an addition rate of 9g for the 7.5 gal water used in 5 gal batches does little to change the pH and even below that it is not as effective as chalk dissolved by CO2. This may explain the recommendation not to exceed an RA of ~250 ppm as CaCO3 when building water.
- Mash thickness effects how much effect the water has on mash pH
This may be a lot to digest right now and in the coming weeks and months I plan to revisit some of the water chemistry and mash pH discussions we had here and on the NB forum.
This comes in the shadow of being accused not to run my own experiments and arm-chair-quarterbacking by a prominent home brewing “celebrity”. What irony and now I can finally take care of that over there.
Acknowledgments go to A.J. DeLange who reviewed an early draft of the paper, gave valuable feedback and whose work on mash pH and water chemistry helped build the foundation for my understanding of the subject.
Prost (I just downed a celebratory half liter of Doppelbock),