Why when brewers refer to acidifying their sparge water, the always refer to targeting a specific pH? Does the acid consume the alkalinity and therefore, alkalinity no longer matters? Is it the alkalinity or the pH which is undesirable, as far as tannin extraction, etc. is concerned?
Sparge water PH
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Temp combined with an Alkaline pH and low mash bed gravity are the culprits to tannin extraction.
Acidify your alkaline water to a neutral pH and you've eliminated a potential for flaw in the finished product and thus no longer need concern yourself with runnings gravities.
Acidify your alkaline water to a neutral pH and you've eliminated a potential for flaw in the finished product and thus no longer need concern yourself with runnings gravities.
As far as I'm concerned, its not pH that matters most. It is alkalinity that matters most for sparge water. Bringing the sparge water alkalinity down to around 20 ppm (as CaCO3) or less is a better target than a specific pH. This is because the starting alkalinity of the tap water affects the final alkalinity of the sparge water if a specific pH target is used. For instance, if a brewer's tap water has modest alkalinity, they might bring the water to a pH of around 6 and have a sparge water with acceptably low alkalinity. However, if the tap water has high alkalinity, they might have to target a much lower pH (say 5.5) in order to end up with an acceptably low alkalinity.
Yes it does but the reason pH is targeted is that if you have a mash at pH 5.3 or so you can rinse it with water as much water at pH 6 as you want and the pH of the runoff will never rise above 6.
In terms of extraction of phenols it is the pH. The higher the pH the more the phenols are dissociated and the more dissociated they are the more soluble they become.
But alkalinity is not a good thing to introduce into your beer at any point in the process. Bicarbonate just doesn't taste that good and added alkalinity in the sparge could keep the kettle pH from going as low as it otherwise would. You get rid of alkalinity when you prepare mash water. Why not treat the sparge water to reduce it at the same time? Easiest way is dilution with RO.
pH and alkalinity are intimately related. If you want to control alkalinity through acid addition (not recommended unless you can tolerate 1 mEq of acid cation for every mEq of alkalinity removed) you do it by setting pH. Some examples:
If you start with water at pH 7 with alkalinity of 50 and acidify with phosphoric acid to pH 5.9 the alkalinity of the acidified water will be 19.5. If you start with alkalinity of 100 the alkalinity after acidification to pH 5.9 will be 37.4. To get the alkalinity down to 19 you would have to acidify to pH 5.5. It's a little different for other acids.
