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Old 12-05-2012, 03:29 PM   #11
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Originally Posted by mabrungard
Those calculations are easily accessible to any brewer via the Bru'n Water software.
Thanks, AJ and Martin. I'm just starting water adjustments (one batch so far) but I've followed the guidance in Bru'n Water.

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Old 03-15-2016, 05:40 PM   #12
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Waking a dead thread here because I'm consistently seeing a strange issue balancing the pH of my sparge water, and this issue seems to belong here.

Background: I use the Brunwater spreadsheet to great effect balancing my mash - whether it's a lager or a porter - really great. I brew on a 3-vessel HERMS system and always start with 12 gallons of sparge water in the HLT regardless of how much I intend to use (most often with a 10g batch I use most of it). I use the Hanna pHep meter with a good/new probe.

I always add the prescribed amount of salts and acid to the sparge and let it mix/recirculate for at least 10 minutes during the temperature ramp to mash-out 170F. What I've noticed is that if I add, say, 1.3cc, and then extract, cool and measure a sample pH at something like 6.2, I want to add a little additional lactic to bring the down to 5.6-5.8. If I then add 0.2cc, wait 5-10mins, extract, cool and measure a new sample, it will have dropped dramatically to something like 4.7 all of a sudden.

Can anyone explain this weird phenomenon? Is the changing temperature of the sparge water affecting the pH (keeping in mind I cool all samples to room temp before using my pH meter)?
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Old 03-15-2016, 09:27 PM   #13
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In going from pH 5.7 (I'll use the average) to pH 4.7 the charge on 1 mmol of carbo (the carbonic, bicarbonate, carbonate system) changes Qc(4.7) - Qc(5.7) = 0.156 mEq/mmol. As 88% lactic acid is about 11 N (each cc releases 11 mEq protons in going to pH's near 5) then the carbo level must be
0.2*11/0.156 = 14.1 mmol (for the whole 12 gal).

So we have 0.2*11/(Qc(4.7) - Qc(5.7) ) = 14.1 for this second change in pH. For the first change you used 1.3 mL of acid which has normality of about 11.7 N (because the pH is a bit higher) and the same formula applies:
1.3*11.7/(Qc(5.7) - Qc(pH?) ) = 14.1 mmol
because the amount of carbo is the same but now the shift is from pH? to 5.7. It doesn't take long to figure that pH? = 9.92 and so if the water you started with had a high pH (even if not as high as 9.92 because we are being pretty approximate) then everything is quite normal. Now, OTOH, if you started with water at pH 7 then things aren't kosher here.
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