As the publishers deadline for the new Water book neared it was realized that a better explanation was needed for the mechanisms that determine and can be used to control mash pH. The material that starts at around p82 resulted and, reading back over it, it does a darn good job. Nevertheless I've had time to think about this more at leisure and come up with the concept of keeping track of 'Proton Deficit' as a convenient way of talking about and predicting what goes on in a mash. If you are a chemist you will know that this is nothing new but just a new twist on 'Proton Condition'. At John's suggestion I presented this idea to the MBAA national conference in Austin compressed into 20 min (John had to work with a worse compression ratio for his talk) and again (in an hour) at the District Mid Atlantic Meeting in Frederick, MD, last weekend. When I got a request for the slides from that later talk it occurred to me that I should make them available to interested readers of HBT as well so this post is to tell you where to find them and that is:
http://www.wetnewf.org/pdfs/Brewing_articles/MBAA_FREDERIC.pptx
I had ginned up a spreadsheet to feed John actual numbers while he was writing like mad and I've dressed that up a bit so that if you really want to see how this works you should play around with that some. It is at:
http://www.wetnewf.org/pdfs/Brewing_articles/MashpH.xlsx
If you do download it and it asks about links to other spreadsheets just click 'ignore' and sail on.
The spreadsheet lets you determine mash pH from a set of malt parameters, water parameters and data on added acids (including phosphoric) and bases. It makes no approximations (other than that of ideally dilute solutions) with regard to the relationships between alkalinity, pH and carbonic acid system proton deficit and it handles the phosphoric acid system in the same way. If you have complete malt data, obtained as is described in the slides, you should get a pretty good prediction (but it is still only a model). Unless you are willing to do a lot of work, you will not have such data but may still like to try this out. For those of you that do I have included Kai Troester's data (which is also in the book) and calculated an approximation to the first malt coefficient (a malt is completely described by its distilled water mash pH and 3 coefficients) which you can stick into the malt parameters section, setting the second and third coefficients to 0. Troester's data was taken without allowance for pH drift with time nor for nonlinearity of the titration curves. The curves are not linear but the deviations from linearity are modest in the pH ranges of interest. I have also included fits from which you can calculate DI mash pH and the first coefficient from the EBC color of the malt. I believe this is what some of the popular spreadheets and calculators do. This is pretty iffy as the fits aren't that good but even this should be better than no data at all.
Because the malts, the carbonic acid system and the phosphate system are non linear closed form solution is difficult so this spreadsheet requires that you put in a pH guess and observe the Total Proton Deficit that guess implies. You then revise your guess in an intelligent fashion (an algorithm is given in the slides) or let the Excel Solver do it for you until you reach 0 proton deficit. The pH which gives you 0 is the estimated pH of the mash. If you are using Excel and don't know what the Solver is you should invest the small amount of time it takes to install it and learn to use it. It is a very powerful tool. OTOH manually guessing and looking at what happens to the proton deficits for each guess should be great for giving you an intuitive feel for where the protons come from and whence they go.
If you want to set mash pH to a given level enter that into the pH field and then adjust water alkalinity, dark malt additions, acid additions... until the total proton deficit is zeroed.
This all seems very simple to me but then I've been close to it for a long time and it wasn't so simple at the outset. I'd be interested to hear what you guys think.
http://www.wetnewf.org/pdfs/Brewing_articles/MBAA_FREDERIC.pptx
I had ginned up a spreadsheet to feed John actual numbers while he was writing like mad and I've dressed that up a bit so that if you really want to see how this works you should play around with that some. It is at:
http://www.wetnewf.org/pdfs/Brewing_articles/MashpH.xlsx
If you do download it and it asks about links to other spreadsheets just click 'ignore' and sail on.
The spreadsheet lets you determine mash pH from a set of malt parameters, water parameters and data on added acids (including phosphoric) and bases. It makes no approximations (other than that of ideally dilute solutions) with regard to the relationships between alkalinity, pH and carbonic acid system proton deficit and it handles the phosphoric acid system in the same way. If you have complete malt data, obtained as is described in the slides, you should get a pretty good prediction (but it is still only a model). Unless you are willing to do a lot of work, you will not have such data but may still like to try this out. For those of you that do I have included Kai Troester's data (which is also in the book) and calculated an approximation to the first malt coefficient (a malt is completely described by its distilled water mash pH and 3 coefficients) which you can stick into the malt parameters section, setting the second and third coefficients to 0. Troester's data was taken without allowance for pH drift with time nor for nonlinearity of the titration curves. The curves are not linear but the deviations from linearity are modest in the pH ranges of interest. I have also included fits from which you can calculate DI mash pH and the first coefficient from the EBC color of the malt. I believe this is what some of the popular spreadheets and calculators do. This is pretty iffy as the fits aren't that good but even this should be better than no data at all.
Because the malts, the carbonic acid system and the phosphate system are non linear closed form solution is difficult so this spreadsheet requires that you put in a pH guess and observe the Total Proton Deficit that guess implies. You then revise your guess in an intelligent fashion (an algorithm is given in the slides) or let the Excel Solver do it for you until you reach 0 proton deficit. The pH which gives you 0 is the estimated pH of the mash. If you are using Excel and don't know what the Solver is you should invest the small amount of time it takes to install it and learn to use it. It is a very powerful tool. OTOH manually guessing and looking at what happens to the proton deficits for each guess should be great for giving you an intuitive feel for where the protons come from and whence they go.
If you want to set mash pH to a given level enter that into the pH field and then adjust water alkalinity, dark malt additions, acid additions... until the total proton deficit is zeroed.
This all seems very simple to me but then I've been close to it for a long time and it wasn't so simple at the outset. I'd be interested to hear what you guys think.