Author Topic: blending two waters  (Read 1023 times)

Offline homoeccentricus

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blending two waters
« on: December 04, 2015, 09:36:11 AM »
A Belgian fellow-brewer would like to know whether there is a relatively simple formula to calculate the mineral/pH properties of the blend of two non-demi waters. The salt content is simply the average of the two waters, I assume?  The pH, when no buffering is present is calculated with the formula log(x) + log(y) = log(xy)? But is there a simple formula to calculate the buffering effect?

I suspect some people will chuckle at this foolishness, and will start throwing terms like "weak acid", "strong base" and "titration" at me, but hey, one can always ask, no?
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Offline pete b

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Re: blending two waters
« Reply #1 on: December 04, 2015, 02:01:32 PM »
I don't know, it seems whenever you have a strange question its for "a friend"
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Offline homoeccentricus

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Re: blending two waters
« Reply #2 on: December 04, 2015, 02:19:40 PM »
I don't know, it seems whenever you have a strange question its for "a friend"

Yes, well, maybe I have set up a "I will answer your embarrassing brew questions for a moderate fee" service.
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Offline kramerog

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Re: blending two waters
« Reply #3 on: December 04, 2015, 03:40:25 PM »
There is probably no simple answer other than who cares.  If your "friend" is blending waters for brewing the pH is generally unimportant.

Offline mchrispen

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Re: blending two waters
« Reply #4 on: December 04, 2015, 04:01:41 PM »
I have a theory. We know that DI water will simply divide the ionic concentrations by the rate of dilution. If you know the composition of both water sources, it should be simply a matter of determining the concentration of each source, based on the ratio of the blend of both sources. So (and I will annotate this incorrectly as, well, because maths):

(SourceA_ion * SourceA_Percentage)+(SourceB_ion * SourceB_Percentage), applied across each relevant ion.

For example:

SourceA_Ca = 100 PPM
SourceB_Ca = 50 PPM
The ration is 1:4, SourceA to SourceB

Then

(100 * .20) + (50 * .80) = Finish_Ca = 60 PPM

If you are concerned about mash pH, then apply this to Total Alkalinity and/or Bicarbonate

You can blend 2 water sources in Bru'n Water by adding your second water source into the table at the bottom of the Water Adjustment. There is a User Custom line reserved - so input the ionic content of the second source, make sure that the Water Report Input page represents the first source. Then you can blend the two on both the Sparge Acidification and Water Adjustment pages - selecting the User Custom (or whatever you named it) drop down and adjusting the dilution percentage.
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Offline homoeccentricus

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Re: blending two waters
« Reply #5 on: December 04, 2015, 04:05:00 PM »
If your "friend" is blending waters for brewing the pH is generally unimportant.
The "friend" wants to write some brewing software  ::)
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Offline homoeccentricus

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Re: blending two waters
« Reply #6 on: December 04, 2015, 04:09:06 PM »
I have a theory. We know that DI water will simply divide the ionic concentrations by the rate of dilution. If you know the composition of both water sources, it should be simply a matter of determining the concentration of each source, based on the ratio of the blend of both sources. So (and I will annotate this incorrectly as, well, because maths):

(SourceA_ion * SourceA_Percentage)+(SourceB_ion * SourceB_Percentage), applied across each relevant ion.

For example:

SourceA_Ca = 100 PPM
SourceB_Ca = 50 PPM
The ration is 1:4, SourceA to SourceB

Then

(100 * .20) + (50 * .80) = Finish_Ca = 60 PPM

If you are concerned about mash pH, then apply this to Total Alkalinity and/or Bicarbonate

You can blend 2 water sources in Bru'n Water by adding your second water source into the table at the bottom of the Water Adjustment. There is a User Custom line reserved - so input the ionic content of the second source, make sure that the Water Report Input page represents the first source. Then you can blend the two on both the Sparge Acidification and Water Adjustment pages - selecting the User Custom (or whatever you named it) drop down and adjusting the dilution percentage.

Yes, I understand the ratio concept  ;) - but it would then also simply apply to bicarbonates. How do you then get the resulting pH? That's a standard formula (see - I know how to put values in Bru'nwater, but don't ask me what they mean  :P )
Frank P.

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Offline mchrispen

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Re: blending two waters
« Reply #7 on: December 04, 2015, 04:45:07 PM »
Without direct measurement, you maybe able to determine a theoretical pH from the alkalinity, but will need to know several other bit of information lacking in our water profiles, such as dissolved Co2. There seem to be several complicated solutions to roughly estimate water pH from alkalinity.

If the brewing software is simply trying to build a model for estimating mash pH from blended water sources, I believe most of the spreadsheets and software are using some form of Kai's model and/or Palmer's model to estimate mash pH... in those cases, the source water pH is ignored and the model uses the alkalinity (or bicarbonate as the non-permanent proxy for alkalinity) as a buffer against the grist acidity & buffering.

http://braukaiser.com/documents/effect_of_water_and_grist_on_mash_pH.pdf

I am out of my water (pun intended) here - so maybe Martin can confirm or correct me. Sorry I couldn't be more help.

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Offline kramerog

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Re: blending two waters
« Reply #8 on: December 04, 2015, 06:14:30 PM »
You could probably get a reasonable pH estimate using the Henderson-Hasselbach equation with carbonates as the relevant ions assuming the use of flat normal drinking water.  I would just use weighted averages of the various carbonates.  This approach is better than averaging pH. Since the pH of blended water is pretty much useless info for brewing, this approach should be good enough.

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Offline reverseapachemaster

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Re: blending two waters
« Reply #9 on: December 04, 2015, 07:32:39 PM »
I'm lazy and hate math that doesn't involve dollar signs so I would figure this out by taking Bru'n Water and changing the RO water profile to the second water profile and let Bru'n Water figure out how the water blends.

But that might not be accurate.
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Offline homoeccentricus

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Re: blending two waters
« Reply #10 on: December 04, 2015, 07:38:17 PM »
Since the pH of blended water is pretty much useless info for brewing

Pardon my obvious stupidity but why is that a priori true?
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Re: blending two waters
« Reply #11 on: December 04, 2015, 08:24:31 PM »
Since the pH of blended water is pretty much useless info for brewing
Pardon my obvious stupidity but why is that a priori true?

Water, regardless of mineralization (within reason), has essentially no pH buffering capacity. The variables that drive mash pH are the water's residual alkalinity and the inherent acidity of the grist. Two water supplies with vastly different pH, used to mash the same grist, could come out to exactly the same mash pH.
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Offline kramerog

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Re: blending two waters
« Reply #12 on: December 04, 2015, 08:27:35 PM »
Since the pH of blended water is pretty much useless info for brewing
Pardon my obvious stupidity but why is that a priori true?

Water, regardless of mineralization (within reason), has essentially no pH buffering capacity. The variables that drive mash pH are the water's residual alkalinity and the inherent acidity of the grist. Two water supplies with vastly different pH, used to mash the same grist, could come out to exactly the same mash pH.
+1.  Mash pH is important, not the pH of the source water.

Offline homoeccentricus

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Re: blending two waters
« Reply #13 on: December 04, 2015, 10:41:22 PM »
So when I plug in my data into Bru'nwater the pH of the water by itself has little or no relevance?
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Offline mchrispen

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Re: blending two waters
« Reply #14 on: December 04, 2015, 10:58:14 PM »
Exactly.

So much more than the simple ionic content we are tracking contributes. CO2 is a contributor and will be absorbed during the mixing process from the air, artificially shifting the pH. Heating to boil (degas) will naturally lower the pH as well and may cause the bicarbonate concentration to shift through conversion of CO2 and potentially the sedimentation of sodium or potassium bicarbonate. Any energy input in the form of mechanical or heat can influence ion concentrations.

My tap water has a nominal pH of 7.6, but a concentration of bicarbonate around 600 ppm. In town, their tap water is 7.5 but the bicarbonate species is <100 ppm.
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