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Old 08-25-2011, 12:36 PM   #1
jaythebassist
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Default Predicting Mash pH with EZ Calculator by Diluting Strike H2O with Lower pH H2O

Is there a way for me to predict a change in mash pH based on adding a specific volume of strike water at a different pH than the rest? I would do this because a. I don't have any 88% lactic acid or acidulated malt on hand, and b. I have a sour mash ready to use (with an unknown acid content).

Example: IIPA

------------

Starting Water (ppm):
Ca: 87
Mg: 15
Na: 28
Cl: 69
SO4: 48
CaCO3: 186

Mash / Sparge Vol (gal): 5 / 4.2
RO or distilled %: 0% / 0%

Total Grain (lb): 16.3

Adjustments (grams) Mash / Boil Kettle:
CaSO4: 0 / 0
CaCl2: 0 / 0
MgSO4: 0 / 4
NaHCO3: 0 / 0
CaCO3: 0 / 0
Lactic Acid (ml): 0
Sauermalz (oz): 0

Mash Water / Total water (ppm):
Ca: 87 / 87
Mg: 15 / 26
Na: 28 / 28
Cl: 69 / 69
SO4: 48 / 93
Cl to SO4 Ratio: 1.44 / 0.74

Alkalinity (CaCO3): 186
RA: 115
Estimated pH: 5.80
(room temp)

---------

Now, I could add 4ml of 88% lactic acid to bring the mash pH down to 5.67 and in the desired range. But I don't have any lactic acid yet (and won't have it in time for my brewday). I do have 3 qts of sour mash that made, and I'd like to use some of that lactic in my mash to get in range. Problem is, I have no idea what acid content it contains.

Hypothetically, let's say I pull a gallon of strike water made up with 104 oz tap & 24 oz of my sour mash (3.5 pH) in it, mix well, and get a pH reading of 7.4. Is there an effective way for me to predict the change in pH that gallon will have on the whole mash? Of course, I know I can just mash in and then keep adding the sour and stirring until the pH corrects, but since I have to wait for the sample to cool, etc, getting the prediction is clutch.

Hope this isn't a ridiculous question to ask.

I guess I could alternatively ask is there an easy way for me to figure out the acid content in my sour mash? (I know the pH reads 3.5 and my tap water is 8.3)

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Old 08-25-2011, 01:18 PM   #2
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The pH of the mix will depend on
1. The alkalinity of the water
2. The acidity of the mash
3. The buffering capacity of the malt

As you don't really know any of these with the exception of the first I'd suggest you make a small test mash and add the sour mash to that incrementally until you reach the pH you want. Then scale up to the full mash. Adding sour mash to grist to adjust pH is a time honored tradition.

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Old 08-25-2011, 01:44 PM   #3
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Quote:
Originally Posted by ajdelange View Post
The pH of the mix will depend on
1. The alkalinity of the water
2. The acidity of the mash
3. The buffering capacity of the malt

As you don't really know any of these with the exception of the first I'd suggest you make a small test mash and add the sour mash to that incrementally until you reach the pH you want. Then scale up to the full mash. Adding sour mash to grist to adjust pH is a time honored tradition.
I gotcha AJ, but aren't numbers 2 and 3 accounted for in the EZ water calculator? That's what I'm asking.. if I manually modify the pH of the strike water how can I get that info into the spreadsheet?
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Old 08-25-2011, 02:05 PM   #4
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The acidity of lactic acid and sauermalz are modeled in the spreadsheet but not your particular sour mash. It's certainly not 88% lactic acid and is probably less than 2% based on sauerrmalz being dry and your mash being wet.

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Old 08-25-2011, 07:29 PM   #5
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Here's a question that can help me get there.. does pH in water dilute in a linear fashion?

Ex: (true or false)

100 oz of 7.0 pH + 12 oz of 1.0 pH = 112 oz of 6.35 pH
-or-
100 oz @ 7.0 pH + 100 oz @ 5.0 pH = 200 oz @ 6.0 pH

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Old 08-25-2011, 07:47 PM   #6
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No, not at all. In the first example lets change oz to mL (the proportions are still the same but the calculations are much easier in metric). If we put 0.1 mol hydrochloric acid in 1 L of water we would have water with pH about 1. 12 mL of this would contain 0.1*12/1000 =.0012 mol H+. Mixed in with 100 mL of water at pH 7 (which contains 0.0000001 mol H+ per liter the total H+ content would be 0.0012/0.112 = 0.0000107143 mol/L for a pH of 4.97. OTOH 100 mL of water at pH 7 contains 0.1* 1E-7 mol and 100 mL of water at pH 5 contatins 0.1*1E-5 for a total concentration of 0.1*1.01E-5/0.2 = 5.5e-7 for a pH of 5.26.

And that's a simple case. If a buffer were involved the ability of acid or base to "pull" the pH depends on the strength of the buffer.

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Old 08-25-2011, 08:54 PM   #7
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Quote:
Originally Posted by ajdelange View Post
No, not at all. In the first example lets change oz to mL (the proportions are still the same but the calculations are much easier in metric). If we put 0.1 mol hydrochloric acid in 1 L of water we would have water with pH about 1. 12 mL of this would contain 0.1*12/1000 =.0012 mol H+. Mixed in with 100 mL of water at pH 7 (which contains 0.0000001 mol H+ per liter the total H+ content would be 0.0012/0.112 = 0.0000107143 mol/L for a pH of 4.97. OTOH 100 mL of water at pH 7 contains 0.1* 1E-7 mol and 100 mL of water at pH 5 contatins 0.1*1E-5 for a total concentration of 0.1*1.01E-5/0.2 = 5.5e-7 for a pH of 5.26.

And that's a simple case. If a buffer were involved the ability of acid or base to "pull" the pH depends on the strength of the buffer.
you had me at "no". lol

I'll go with the test mash.
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