Originally Posted by BigEd
It's not just about the pH! Time again I have seen people obsess about the pH without considering the other factors involved in the process that determines what the pH is. IMO rather than force the pH of your water down with additions for light beers you would be much better off de-alkalizing or diluting your water to begin with a lower RA.
There are 2 parts to water treatment. The first is getting the pH right. This is a sine qua non
- don't do it right and you won't have the best beer you can. The other part is getting the "stylistic" ions right. The two goals are not independent. For example, if you have high alkalinity and want to increase chloride you can neutralize with hydrochloric acid. If you want high sulfate you can neutralize with sulfuric acid. If you want soft water beer (Pils) you cannot neutralize with acid because when you do this the source of alkalinity, bicarbonate, is replaced with the anion of the acid you choose.
HCO3- + HCl --> H2CO3 + Cl-
2HCO3- + H2SO4 --> 2H2CO3 + SO4--
As an example if you had water at pH 7 with alkalinity of 100 (bicarbonate 120) and calcium of 39.44 (enough to balance the bicarb if nothing else is present) the RA would be 71.9. If you added enough sulfuric acid to lower the pH to 5.6 (the distilled water pH of Maris Otter ale malt) the alkalinity would drop to 19, the residual alkalinity to -9 and the bicarbonate to 22 but the sulfate would be 77.3 mg/L. If mashing with this treated water additiona acid (such as lactic) would be wanted to get the mash pH down to 5.4. At this point only 14.8 mg/L bicarbonate would remain and these lost bicarbonate ions would be replaced by lactate ions. The calcium would remain at 39.44.
Acidification gets rid of most but not all of the alkalinity. If the example water had alkalinity of 200 (and calcium equal 78.88mg/L) the amount of bicarbonate remaining in the mash after acidification with acid would be 29.6 and so on. As bicarbonate does have a negative flavor effect the less of it there is in your beer the better.
An alternative way to reduce alkalinity is dilution. 4 + 1 dilution of this hypothetical water with DI would reduce alkalinity to 20 without any addition of sulfate. The pH would stay (almost0 the same so the bicarbonate will be a little higher at 24 but no sulfate is introduced. Note that the calcium also down by a factor of 5 (to 8) and so, if you wish to fully restore that you will have to add back calcium chloride or calcium sulfate which gets you more or less back to where you were with the acid i.e. with cation equivalent (equivalence has specific meaning in chemistry) to the alkalinity you removed. But you may choose to forgo that. Fine beers are brewed with calcium levels that low.
It should be clear that this can all be tricky in the details and thus such considerations are exactly the opposite of the KISS that I largely preach. As it appears the best beers come from the softest water the dilution approach seems to have a lot of merit. Exception: when high sulfate is wanted.