sparging water acidification

[matc]

I'll be brewing a stout soon usung ro water. I'll add minerals using brun' water and was wondering if I need to acidify my sparge water ? In brun' water, it mentions that it is not necessary to add acids to the sparge water if using 100% ro water. In which cases adding an acid is a must ?

 

[Yooper]

I'll be brewing a stout soon usung ro water. I'll add minerals using brun' water and was wondering if I need to acidify my sparge water ? In brun' water, it mentions that it is not necessary to add acids to the sparge water if using 100% ro water. In which cases adding an acid is a must ?

If you're using 100% RO or distilled water, there is no reason to add acids to the sparging water. If the water is not RO and has moderate to high alkalinity, it will be necessary to acidify the sparge water.

 

[mabrungard]

The purpose of acidifying your sparging water is to reduce its alkalinity. That reduction in alkalinity can be somewhat assessed by a reduction in pH. Many brewers target a specific pH for their sparging water, but that can be a little inexact since the water's starting alkalinity actually has an influence on the remaining alkalinity in the water...even when you have targeted the same pH. Brewer A with somewhat low starting alkalinity only has to target a pH of say the middle 5's. But Brewer B with really high alkalinity would still be left with a lot of alkalinity in the acidified water if they targeted that same pH. Higher your starting alkalinity, the lower the pH you need to target.

 

[ajdelange]

Brewer A with somewhat low starting alkalinity only has to target a pH of say the middle 5's. But Brewer B with really high alkalinity would still be left with a lot of alkalinity in the acidified water if they targeted that same pH. Higher your starting alkalinity, the lower the pH you need to target.

Both, in order to completely remove the effects of sparge water alkalinity, should adjust the pH of the sparge water to the vorlauf pH irrespective of whatever the source water alkalinity and pH might have been. If vorlauf pH is 5.3 there is no way that pH 4.3 sparge water can raise the pH of the runoff above 4.3 just as there is no effect from mash water which has been acidified to the desired mash pH will influence mash pH.

It actually makes more sense to acidify sparge water to the desired kettle pH.

Alkalinity cannot properly be spoken of with out specifying the starting and end point pH's. When your water report says alkalinity is 100 that means that the lab took your water at whatever pH it came to them and added 2 mEq/L acid in to order to reach the end point of their titration (probably pH 4.5). Alkalinity is the amount of acid required to reach the end point. Thus if you are shooting for a mash pH of pHz and acidify your sparge water to pHz the 'alkalinity' of your sparge water with respect to pHz is 0, whatever the original pH or alkalinity.

Suppose Brewer A has pH 7 water with low alkalinity (1 mEq/L ~ 50 ppm RE pH 4.5). If he targets pHz = 5.2 for kettle pH he would have to add acid to the extent of 0.94 mEq/L in order to negate the effect of the water on mash pH. If he did that and sent the treated water off for analysis the report would come back that the sample had alkalinity of 0.06 mEq/L (3 ppm). Thus, apparently acidifying this water to pH 5.2 resulting in 0 alkalinity WRT that pH removes 94% of the alkalinity WRT pH 4.5. But that remaining alkalinity is immaterial unless he changes his mind and decides to shoot for, say pHz = 5.1 in which case he would have to add another 0.01 mEq/L (1 ppm as CaCO3).

Suppose Brewer B has pH 8.4 water with higher alkalinity (5 mEq/L ~ 250 ppm wrt pH 5.4). If he also adjusts to pH 5.2 he will require 4.8 mEq/L acid (unsurprisingly enough about 5 times as much as Brewer A). If he also sends the treated water off to the lab his alkalinity report will come back at somewhat less than 0.2 mEq/L ~ 10 ppm (less than this because at pH 5.2 most of the carbo will have converted to CO2 and will escape to the air unless prevented from doing so). If he too changes his mind and decides he wants 5.1 then he will need another 0.06 mEq/L (again about 5 times as much).

Now if Brewer A decided, for whatever reason, to acidify only to pH 5.5 he would still have an alkalinity wrt 5.2 of 0.067 mEq/L whereas if Brewer B acidified to that same pH he would have remaining alkalinity of 3.54. To get the same residual 0.067 he would have to acidify to pH 5.29.

This has looked at sparge water pH from the POV of maintaining proper kettle pH for which the acid has to be added at one point or another by the time the wort is in the kettle. Keeping runoff pH is also, of course, important. If Brewer B adds the 4.48 mEq/L he must add to get to pH 5.5 he is protected against phenol uptake from husks but he will need to add more acid (0.27 mEq/L) later if he wants kettle pH 5.2.

To try to summarize: a brewer should add as much acid to his sparge water as is necessary to get to the desired kettle pH irrespective of alkalinity of the sparge water if influence on kettle pH is the goal. If getting the sparge runoff pH below 6 is the only concern he may add acid to any pH < 6 he desires.