[gordonstrong]

Maybe 1/4 to 1/2 a tsp in 5 gallons of RO water.

You don't have to add acid willy nilly.  Bru'n Water includes AJ DeLange's very capable water acidification calculator.  If you know your water profile, the acid type and strength, you can calculate what your addition is fairly precisely.  I've been using that calculator for a decade and its correct every time.

It's not willy nilly.  It's until I hit a certain pH target.  It's just that the amount of acid varies since RO water doesn't always have the same mineral profile.  The problem is that I don't know my water profile every time.  It changes.  So rather than analyzing my water every time I use it, I measure the pH, which is what I really care most about anyway.

[narvin]

So, using phosphoric acid results in an insignificant amount of phosphate compared to what's already in the mash.  Seems like this would have no flavor impact on the finished beer.   What's the advantage of using slaked lime to remove bicarbonates instead?  Seems like a lot of work (precipitating the chalk overnight, racking off of it) for a process that also removes Calcium.

[tschmidlin]

So, using phosphoric acid results in an insignificant amount of phosphate compared to what's already in the mash.  Seems like this would have no flavor impact on the finished beer.   What's the advantage of using slaked lime to remove bicarbonates instead?  Seems like a lot of work (precipitating the chalk overnight, racking off of it) for a process that also removes Calcium.

I'm not sure I understand your question . . . you would use them for different reasons.  Adding phosphoric acid will drop the pH.  Adding slaked lime will raise it.

Slaked lime is calcium hydroxide, so you are adding calcium anyway.  If the increase in pH precipitates CaCO3, well, one of the water chemists can probably explain if there is a net increase/decrease/no change in the amount of calcium, I don't know.

[gordonstrong]

Slaked lime is sometimes used to precipitate temporary hardness from water.  It's an alternative to boiling.  I have horrible water, full of carbonates.  That's what I get for living on top of a huge chunk of limestone.  So I've tried all sorts of things, including both methods.  They take time, energy, and labor.  And they still aren't all that effective.  So I solve the problem by buying RO water.

I use phosphoric acid to adjust the pH of RO water.  Yes, adding lime to water with temporary hardness will lower pH because of the reactions that result in precipitate.  Just like adding gypsum to a mash lowers pH because of the reactions it causes.  But if you have RO water, there is nothing to react with.  The only way you lower pH is to add an acid.

So I add an acid when I want to lower the pH.  If I wanted to change the mineral content, then I'd do something else.

I'm more interested in engineering beer than engineering water.  What happens along the way is of less concern to me as long as the outcome is something I can predict and control.

[mabrungard]

So, using phosphoric acid results in an insignificant amount of phosphate compared to what's already in the mash.  Seems like this would have no flavor impact on the finished beer.   What's the advantage of using slaked lime to remove bicarbonates instead?  Seems like a lot of work (precipitating the chalk overnight, racking off of it) for a process that also removes Calcium.

Slaked Lime actually significantly increases water alkalinity initially.  It is added to increase the pH of the water to above 10 where calcium carbonate becomes insoluble.  Increasing the pH to above 11 will also reduce the solubility of magnesium.  That undesirable hardness precipitates out of solution and the clear water is decanted off the sediment.  

That clear water still has significant alkalinity.  Either CO2 is bubbled through the water to help reduce the water pH (it adds carbonic acid) or an acid such as hydrochloric, sulfuric, phosphoric, or lactic is added to bring the pH (and alkalinity) to a reasonable level.  

This process is only partially effective at removing calcium or magnesium.  If the water had mostly temporary hardness, you can typically only bring the Ca to 30 ppm and the Mg to 10 ppm with Lime softening.  If it has a lot or permanent hardness, then the Ca and Mg will be higher.

Phosphororic acid is relatively tasteless in beer for the reason you cite.  

Unlike Gordon, I am interested in both engineering water and beer.  In both cases, they are my profession.

[narvin]

I'm really just looking for alternatives to carting home 15 gallons of RO water when I want to brew a pilsner.  It's mostly the bicarbonates I want to eliminate, since the other mineral levels are fine for a German pils.  I have 10% phosphoric acid that I bought from NB a few years ago... never used it much thanks to some "advice" that's been going around