Author Topic: pH questions  (Read 1799 times)

Offline ccfoo242

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pH questions
« on: March 11, 2012, 02:57:36 PM »
Today was my 3rd all grain brew and I have some questions regarding mash pH, pre-boil pH, and post-boil pH.

I brewed an oatmeal stout (the one in Brewing Classic Styles) so my grain bill looked like this:
9.4 lbs british pale ale malt
1 lbs oats (toasted in the oven)
12 oz chocolate malt
12 oz victory malt
8 oz black barley
8 oz crystal 80

I used the Bru'n Water spreadsheet to calculate my water additions, using Black Balanced as my target.

I diluted my filtered tap water with 50% distilled which gave me a starting water profile like this:
Calcium 39.0
Magnesium 17.0
Sodium 19.0
Sulfate 82.5
Chloride 38.5
Bicarbonate 67.0
Cations 4.2
Anions 3.9
Total Hardness 167
Alkalinity 55   
RA 18
SO4/Cl ratio 2.1

My mash water volume was 3.7 gallons. I added 0.4g baking soda and 1.5g pickling lime to arrive at this:
Calcium 96.1
Magnesium 17.0
Sodium 26.2
Sulfate 82.5
Chloride 38.5
Bicarbonate 260.1
Cations 7.3
Anions 7.1
Total Hardness 310
Alkalinity 215
RA 137
SO4/Cl ratio 2.1

Additionally, I added 3g gypsum, 1.6g calcium chloride, 2.9ml lactic acid to the sparge water, per the spreadsheet.

The estimated room temperature mash pH was 5.3.

After 15 minutes of mashing, I stirred the mash then took a sample from the top.
pH at 15 minutes was 5.8 at 70F

pH of 1st runnings was 5.5 at 70F
pH of pre-boil wort was 5.5 at 70F
pH of post-boil wort was 6.5 at 70F <--- ???

Do these pH numbers look appropriate?  I checked my meter prior to brewing with 4 & 7 calibration liquid and
 it was fine.

If I remove all of the darker grains from the spreadsheet the estimated pH shoots up to 6.4. Is it possible that the spreadsheet is overestimating the dark malt's pH lowering magic (yes, it's magic, at least until I understand it! :-)
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Offline narvin

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Re: pH questions
« Reply #1 on: March 11, 2012, 03:36:05 PM »
Did you measure the pH before adding the pickling lime?  Given that very small amounts can cause large pH shifts, I wouldn't use it unless I knew I needed it. 

When it comes to water modification (and especially alkalinity), less is more.  Overdoing salt additions is an easy mistake to make.  I've found that spreadsheets do overestimate alkalinity needed to balance dark malts, although Kai's less so than Bruin water.
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Offline mabrungard

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Re: pH questions
« Reply #2 on: March 11, 2012, 04:53:01 PM »
All of the pre-boil numbers look fine.  You should typically see another tenth or two pH drop after boiling.  It looks like your instrument is decieving you.  I don't know of a situation that could cause the pH to rise after boiling.
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Offline ccfoo242

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Re: pH questions
« Reply #3 on: March 12, 2012, 11:21:48 AM »
You're probably right about that last reading. The sample that reading came from was sitting out for over an hour while I was doing other things before I remembered to check it. Not sure if that can effect things or if my meter needed to be recalibrated that soon.  When I take a sample next week to check gravity I'll check the pH again. (it's fermenting just fine already)

Questions:
  • Does water to grist ratio effect mash pH? I had a rather thick mash (1.1qt per pound I think).
  • Does it matter if I add salts to the water while I'm bring up to strike temp or do I throw them in after mash-in?  I've been adding to the water while it heats up.
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Offline mabrungard

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Re: pH questions
« Reply #4 on: March 13, 2012, 12:20:14 PM »
Questions:
  • Does water to grist ratio effect mash pH? I had a rather thick mash (1.1qt per pound I think).
  • Does it matter if I add salts to the water while I'm bring up to strike temp or do I throw them in after mash-in?  I've been adding to the water while it heats up.

The water/grist ratio can have an effect on mash pH.  This effect can be large when the brewing water has significant alkalinity. 

There is a reason for that effect.  The interplay of acidity from the grist and alkalinity from the water typically provide a net increase in the acid content to the mash and the mash pH is therefore driven down in comparison to the water's starting pH.  A closer look at the mash system is presented below.

A grist of a certain size and composition (percentages of base, crystal, and roast malts) is going to produce a certain quantity of acidity that can be expressed in milliequivalents (meq) of acid.  For example, Base malt might provide 1 meq per lb, while Crystal 40L and 120L provide 11 and 28 meq per lb, respectively.  Roast malts provide a relatively consistent acidity of about 19 meq per lb regardless of their degree of roasting.  Its a fairly easy task to add up all the acidity contributions from the grist components to determine the total acidity of the grist.  That is what Bru'n Water does. 

We know that typical water has a degree of alkalinity and that it varies with the water source.  Many of us also know that calcium and magnesium ions interact with the grist to produce malt acids that moderate the water's alkalinity.  That is the basis for the Residual Alkalinity concept.  Since we know that residual alkalinity is a valid response in a mash system, we can use it as a basis of calculating the net alkalinity provided by the water in the mash.  So for a case where the water provides a residual alkalinity of 50 ppm, that provides 1 meq alkalinity per liter of water.  Multiplying that result with the total number of liters of mashing water and you have the milliequivalents of alkalinity that will neutralize a portion of the grist acidity. 

Since the size of the grist is dependent upon the desired starting gravity of the wort, it will stay constant along with the total meq of acidity from the grist.  But, you should now see that the quantity of water added to the mash is going to determine how much alkalinity will be added to the mash to neutralize some of the grist acidity.  A thinner mash adds more alkalinity while a thicker mash adds less alkalinity.  More alkalinity means the mash will have a higher pH and less alkalinity means a lower mash pH will be produced.

The information above was just one example, but it illustrates that mash thickness can be used as a variable to help attain a desirable mash pH.

Regarding when to add minerals to the water, all of the minerals we typically brew with are more soluble in cooler water.  So adding them early, before the water is really hot is going to improve their solution.  The good thing is that almost all of them are very water soluble.  Its only chalk that has poor solubility.  It should be added when the water is cool.  Unfortunately, we also know that chalk needs acid to help it dissolve.  That is why we add chalk directly to the mash, even though the mash is hot.  The malt acids help dissolve the chalk.  Unfortunately, those malt acids are not enough to fully dissolve chalk.  So don't count on its full alkalinity contribution. 

Enjoy!     
« Last Edit: March 13, 2012, 12:25:38 PM by mabrungard »
Martin B
Carmel, IN

BJCP National
Foam Blowers of Indiana (FBI)

Brewing Water Information at:
https://sites.google.com/site/brunwater/

Like Bru'n Water on Facebook for occasional discussions on brewing water and Bru'n Water
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