Author Topic: "Measured" or "Reported" pH Value for Water Calculator?  (Read 450 times)

Offline philm63

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"Measured" or "Reported" pH Value for Water Calculator?
« on: June 22, 2014, 06:30:47 AM »
Just got this year's water report from Ward Labs and it says my pH is 7.9. Each time I brew, I take measurements of the water I use for brewing and record it on my brew log. I use filtered tap water (city water - very low minerals - typical under-sink canister-type filter, changed regularly) and each time I take a measurement, I come up with around pH 6.0, not the 7.9 Ward labs says.

Not sure how our measurements differ, I assume they do differ as we're getting very different results, but what I'd really like to know is if I should be inputting into the water calculator what I measure here, or what Ward Labs measures there? pH 6.0 vs. pH 7.9 makes a big difference in what shows up in Bru'n Water. NOTE - I calibrate using 2 points each time I use my MW101 pH meter so I'm reasonably sure my readings are good.

Could atmospheric contamination be making that big of a difference in what I measure? Did Ward Labs draw a small sample off my sumitted sample and purify it under a vacuum or inert gas to get their pH reading?
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Offline hopfenundmalz

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Re: "Measured" or "Reported" pH Value for Water Calculator?
« Reply #1 on: June 22, 2014, 06:39:31 AM »
CO2 diffusing into water drops the pH. I don't know if that is the total explanation here. Maybe Martin can give more insight on this difference.
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Offline Kinetic

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Re: "Measured" or "Reported" pH Value for Water Calculator?
« Reply #2 on: June 22, 2014, 06:55:00 AM »
What does your city say about the water's pH?  Most city water will be in the 7-8 pH range.  I doubt your tap water is 6.0. It sounds like your pH meter isn't right.  You said you calibrated it.  Are you sure the calibration solutions are right?  They can expire.  They can become contaminated.



Offline mabrungard

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Re: "Measured" or "Reported" pH Value for Water Calculator?
« Reply #3 on: June 22, 2014, 07:17:28 AM »
It is possible that some tap waters have low pH. That is most likely for sources that have very little alkalinity in their water. With that said, tap water pH has very little to do with subsequent brewing water chemistry. The most important factors are the actual ionic content and the critical ions that affect mashing pH: Ca, Mg, and HCO3. If those ion concentrations accurately represent what is in the water, then a brewing chemistry program has a decent chance of predicting pH for the user.

In the case of a difference between a Ward report and tap water, tap water is more likely to contain more dissolved CO2 since it was under pressure in the distribution piping system. If you leave a sample out and its pH rises over several hours, it is a likely sign that the water has excess CO2. If the pH falls over time, then its a sign that the water has little alkalinity and little dissolved CO2.

I guess it is possible that Ward vacuum degasses the samples they receive, but I don't know. I don't recall if degassing is a required protocol for testing. 
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Offline philm63

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Re: "Measured" or "Reported" pH Value for Water Calculator?
« Reply #4 on: June 22, 2014, 07:37:06 AM »
So would it be best to input what I actually measure into Bru'n Water instead of the reported value as I had done in the past?
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Offline mabrungard

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Re: "Measured" or "Reported" pH Value for Water Calculator?
« Reply #5 on: June 22, 2014, 09:19:56 AM »
So would it be best to input what I actually measure into Bru'n Water instead of the reported value as I had done in the past?

pH has only a small effect on the sparge acidification calculation. Check it out, vary the pH input and you should see only a small variation in the amount of acid added.
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Online Jimmy K

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Re: "Measured" or "Reported" pH Value for Water Calculator?
« Reply #6 on: June 22, 2014, 10:14:28 AM »
I'm also thinking that as you heat water for mashing it will off-gas dissolved CO2, so the pH of strike water will be higher.
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Offline macbrews

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Re: "Measured" or "Reported" pH Value for Water Calculator?
« Reply #7 on: June 22, 2014, 10:47:08 AM »
I have the same issue with my water, but as Martin said, it has little effect on my mash pH.  I have been using Bru'n Water and my calculations are spot on when I check my mash. (same meter too)

I'll try leaving it out for a bit and then check to see if it rises from the CO2 dissipation.

Mac

Offline philm63

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Re: "Measured" or "Reported" pH Value for Water Calculator?
« Reply #8 on: June 22, 2014, 12:51:41 PM »
Perhaps I'm chasing something that doesn't need to be caught. As Martin said, the pH of the base water has little effect compared to the ions (existing or added), and so far as I can tell I've been pretty close or dead-on hitting predicted mash pH. I also checked his remark that even if you change the pH in the water analysis input, it does very little downstream, which I confirmed. Chase over. Thanks to Martin et al.
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