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Old 01-30-2013, 02:24 AM   #1
bleak
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Default Phosphoric acid recommendations

This has probably been covered before, but I didn't come up with anything pertinent when I searched. John Palmer's book states that Phosphoric acid is not recommended for lowering mash pH, because it reacts chemically with calcium in the mash and changes the whole playing field, rather than simply adjusting the pH. Obviously Phosphoric acid has been recommended here many times, and I was wondering if Palmer is simply mistaken, or is overstating the reaction with calcium. Among those here who swear by Phosphoric, what are your thoughts about what Palmer says?


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Old 01-30-2013, 04:05 AM   #2
ajdelange
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It is true that calcium phosphate is extremely insoluble but it is also true that at mash pH very, very little of inorganic phosphate is in the phosphate form. Nevertheless we do rely on precipitation of phosphate with calcium to lower the pH of our beer whenever we rely on the phytin reaction with calcium to provide some or all of the protons we need to reduce mash pH. Put another way there is so much phosphate in mash (a percent or so of malt weight is phosphate) that a little more from acid isn't likely to result in appreciable extra stripping of calcium which would be the main concern. I do calculate saturation WRT apatatite ( the most likely form of calcium phosphate) in my spreadsheet. It seems to me that for a typical problem the calcium level has to be above 150 for there to be precipitation from added acid but I'm relying on memory here which is a little risky.

Probably the most relevant piece of information at hand is that Sierra Nevada acidifies all their brewing water with phosphoric acid.
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Old 01-30-2013, 05:41 AM   #3
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Thanks, that helps a lot.
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