Mash pH calculations off by .3!

[renthispace]

I purchased a Hach Pocket Pro+ a month ago and yesterday I finally got a chance to use it during my brew (with a 3-point calibration right before). This was my first brew that I have tried to track mash pH and use brewing salts. I used Brewersfriend for all my calculations, but since have double checked with Bru'n'water, EZ Water Calcs, and Kaiser Water Calcs. All are relatively close and show that I need to add a good amount of acid to get a mash pH of 5.3. I used a <b>third</b> of the required acid (20ml of 10% phosphoric acid) and undershot my pH and reached 5.25! Since the calculators are all estimating about the same mash pH, I'm assuming I did something wrong. Hopefully one of you can help me figure out what I did.

The only thing I have found that I should have differently is adding the acid to the cold mash. I added (and mixed it) to my mash in water while it was 159F. Now onto the numbers.

My water is variable (bay during winter, reservoir during summer) so I knew my water report wouldn't be spot on during any particular brew during the year. I purchased a GH & KH test kit (the same one used here: http://braukaiser.com/wiki/index.php?title=At_home_water_testing ) to try and get a current reading of the important ions. GH took 6 drops, KH took 7. I took those numbers and used the converter to translate into ppm of calcium, magnesium, and alkalinity. I used the averaged numbers from my water report for the sodium, sulfate, and chloride concentration. I used my pH pen to find the pH of the water. The following is the water profile I used:

Calcium: 35
Magnesium: 9
Sodium: 49
Sulfate: 40
Chloride: 76
Alkalinity: 125 as CaCO3
pH: 8.65


I use BIAB so my total water was 8.1 gallons with no sparge. The °L may be different than what I bought as I did not record the values when I purchased the grain from the brew shop. The values are what brewersfriend put in for the grains I used.

Amount__Fermentable_____________________PPG__°L___ Bill %
10 lb____United Kingdom - Maris Otter Pale___ 38___3.75__75.5%
1 lb_____German - Munich Light_____________37___6____7.5%
0.5 lb___Belgian - CaraVienne_______________34___20___3.8%
0.5 lb___German - Abbey Malt_______________33___17___3.8%
0.5 lb___German - Carapils_________________35___1.3___3.8%
0.5 lb___American - Caramel / Crystal 60L____34___60___3.8%
0.25 lb__American - Chocolate_______________29__350___1.9%
13.25 lb Total

Since my ions were already fairly in range I didn't want to add much salt to try and lower the pH (brewersfriend estimated mash pH at 5.72, EZ Water 5.78). I only added 1 gram of gypsum. To reach 5.4, brewerfriend estimated 64ml of phosphoric acid would need to be added! Kaiser's spreadsheet ~66, Bru'n'water 70ml. This seemed like a lot so I figured to only add 20ml and then test 15 min into the mash to see if further adjustments were needed...glad I did!


As I said before, I did add the acid while the water was hot so maybe that was my issue? I tested the mash at 15 minutes in and it read 5.4 at 85F. As the temp dropped, so did the pH. When it stabilized at room temperature I was at 5.25 (about 10 minutes later). I'm so glad I did not add 60ml of acid! I tested the mash pH again at the end of the mash and this time I quickly cooled the sample to room temperature for a reading of 5.25.

So what could have happened? I've been playing around with the calculators trying to recreate my observations and I don't get why I'm so far off from the predictions. I'm thinking I should send a water sample in to verify if my above estimated profile is indeed my current water profile. What am I missing?

 

[JonM]

The Lovibond ratings for the grain isn't always what's listed. I bet something was a touch darker than expected and contributed a touch more acidity.

I've always understood that the software gets you "in the ballpark" and that you're almost always going to have some fine tuning to do once the mash is underway.

 

[renthispace]

Agreed, however even adjusting the lovibond for my base malt and the darkest malt (both up and down...I figured these two were the biggest adjusters of pH) did not change the mash pH in the magnitude that I'm off. It was like +-5ml of acid (from 65ml) when I varied the lovibond.

I should have only added ~15ml of acid to reach mash pH of 5.4 and so far I can't figure out why these calculators have me so far off.

 

[McKnuckle]

Brewer's Friend states:

"mash [pH] prediction is for mash sample cooled to 25 C / 77 F"

 

[ajdelange]

I purchased a Hach Pocket Pro+ a month ago and yesterday I finally got a chance to use it during my brew (with a 3-point calibration right before). This was my first brew that I have tried to track mash pH and use brewing salts. I used Brewersfriend for all my calculations, but since have double checked with Bru'n'water, EZ Water Calcs, and Kaiser Water Calcs. All are relatively close and show that I need to add a good amount of acid to get a mash pH of 5.3. I used a <b>third</b> of the required acid (20ml of 10% phosphoric acid) and undershot my pH and reached 5.25!

The first thing you do when you get a pH meter reading that doesn't look right is rinse the electrode in DI water and go back into the 4 buffer. Most of the time you will find that the meter has been improperly calibrated or has drifted for a variety of possible readings. We hope you did the stability check (as described in https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/ since Hach has been known to ship units that do not pass it).

Since my ions were already fairly in range I didn't want to add much salt to try and lower the pH (brewersfriend estimated mash pH at 5.72, EZ Water 5.78). I only added 1 gram of gypsum. To reach 5.4, brewerfriend estimated 64ml of phosphoric acid would need to be added! Kaiser's spreadsheet ~66, Bru'n'water 70ml. This seemed like a lot so I figured to only add 20ml and then test 15 min into the mash to see if further adjustments were needed...glad I did!

You have a lot of water relative to the amount of grain and that water is fairly alkaline at 2.5 mEq/L (divide by 50). To get just the water to pH 5.4 you will need 70 mEq of acid. The other major proton absorber is the base malt. Assuming that MO has a mash pH of about 5.6 and typical buffering that will require another 45. I don't have any of the details of the colored malts but guessing as to their properties it would seem that you would have a total deficit of about 75 mEq to be made up for by added acid. Since 10% phosporic acid is approximately 1.09 N at pH 5.4 you would need 75/1.09 =68.6 mL of 10% phosphoric to do the job.

As I said before, I did add the acid while the water was hot so maybe that was my issue? I tested the mash at 15 minutes in and it read 5.4 at 85F. As the temp dropped, so did the pH. When it stabilized at room temperature I was at 5.25 (about 10 minutes later).

It doesn't much matter when you add the acid but it does matter when you read it. All the calculations I'm giving here are at room temperature. If you added 1/3 the requisite 69 mL (i.e. 33 mL) your mash pH was probably about 5.6. The fact that you read 5.25 squarely focuses the light on the pH meter. My suggestion is, therefore, that you look at the meter and do the cal stability check.

 

[Wynne-R]

Is the acid really 10% ?

I was getting really wacky results with 10% Lactic acid, high and low. A chemist told me I should stir the acid before I use it. Apparently the water would separate out giving me random strength when I poured it.

It worked for me.

 

[mabrungard]

A chemist told me I should stir the acid before I use it. Apparently the water would separate out giving me random strength when I poured it.

Hmm??? I never thought of that. I know that phosphoric acid has a higher specific gravity than water and I know that lactic acid has a 'viscosity' that might limit how well it mixes with water. But I've not heard of an acid separating from water.

AJ, have you heard of this phenomena?

 

[ajdelange]

Not for a 10% solution of phosphoric acid nor for strong solutions of phosphoric or lactic but strange things can happen when solutions of other wise highly soluble solids are involved. Have a look at the phase diagram in the Calcium Chloride Handbook, for example.

 

[renthispace]

Thanks for your input AJ.

I did do a meter calibration test when I first got it. I think I saw the pH rise about .01 per hour following calibrating it. I didn't record/plot my results but they seemed consistent with reports from others on this meter.

Great idea on the verification of the calibration for the meter. That is one thing I did not check following the calibration. Now that I'm a few days after pitching the yeast, can I do another test on the beer or will the pH have moved from when I mashed from the boil and fermentation process?


One big question that I have in regards to the calibration process regards the temperature. So this probe has ATC, but how does that work when the calibration solution of 4.01 is 4.01 @ 25C and it is being calibrated at 18C? Will the ATC part know that the calibration solution is a different pH at 18C?

When I was first playing with my meter, the pH read for each calibration solution was off (as expected--this is why I'm calibrating). After waiting for the meter to stabilize I confirmed the reading and moved to the next buffered solution. After the meter was calibrated I put it back into the pH 4.01 buffer. Since I was in my garage I was at 18C and not the 25C that the 4.01 buffer is rated for. Instead I think the meter read 3.99. The bottle had the different pH written for different temperatures and the value interpolated for the current reading. This is normal procedure correct?


Thanks for double checking the math and expected amount of acid. The only thing that makes sense at this point is the meter wasn't correctly calibrated. It just strikes me odd as I did the exact procedure that I've done before (and verified). I just wish I would have verified it during the brew to really know what happened.

 

[ajdelange]

Great idea on the verification of the calibration for the meter. That is one thing I did not check following the calibration. Now that I'm a few days after pitching the yeast, can I do another test on the beer or will the pH have moved from when I mashed from the boil and fermentation process?

Yes, both the boil and the fermentation will have dropped the pH appreciably. As you learn more about pH in brewing you will start measuring pH both at the beginning and end of the boil (don't forget to cool samples) and early on in the fermentation as a pH drop is a sure indicator that the fermentation is underway before any other signs show this.

One big question that I have in regards to the calibration process regards the temperature. So this probe has ATC, but how does that work when the calibration solution of 4.01 is 4.01 @ 25C and it is being calibrated at 18C? Will the ATC part know that the calibration solution is a different pH at 18C?

Yes it does. In the pH calibration sticky the two formulas that the meter uses to calculate the pH of the buffer given the temperature are included.

When I was first playing with my meter, the pH read for each calibration solution was off (as expected--this is why I'm calibrating). After waiting for the meter to stabilize I confirmed the reading and moved to the next buffered solution. After the meter was calibrated I put it back into the pH 4.01 buffer. Since I was in my garage I was at 18C and not the 25C that the 4.01 buffer is rated for. Instead I think the meter read 3.99. The bottle had the different pH written for different temperatures and the value interpolated for the current reading. This is normal procedure correct?

Yes and a meter with properly functioning ATC will read what the bottle says the pH should be at the temperature in question. Proper functioning of ATC depends on the electrode having an isoelectic pH (the pH at which it's response is not dependent on temperature) of 7.00. It is assumed these days that electrodes all have an isoelectric pH close to 7.00 but I am on my second one which has pHi greater than 8. That's not a problem for me as I just put the correct pHi into the algorithm but I know of no meter that allows you to do this and that is why I always recommend having buffers and samples at as close to the same temperature as possible. This makes less demands on ATC and if your pHi is indeed off a bit that doesn't matter.

Thanks for double checking the math and expected amount of acid. The only thing that makes sense at this point is the meter wasn't correctly calibrated. It just strikes me odd as I did the exact procedure that I've done before (and verified). I just wish I would have verified it during the brew to really know what happened.

There is a learning curve.

 

[renthispace]

So I was going to recalibrate my meter when I decided to see how far off it currently was. pH 4 buffer read 4.01 @17C (bottle says 4.00) and pH 10 buffer read 10.09 @ 17C (bottle says 10.08 when interpolated).

Amazing my Pocket Pro is only .01 off from calibration that I did two days ago. Meaning my readings were likely correct? Anyway I read the pH of the fermenting beer and it was 3.91 @18.6C!

So either my GH & KH test kit steared me wrong or maybe my grain bill is different than what I thought? Still seems like I'm off _a_lot and these two issues would only account for minor error (as one would expect there to be).

 

[mabrungard]

Wait! Why are you calibrating with 4 and 10 solutions? For the typical pH range in brewing, you should calibrate with 4 and 7 solutions. The way you are calibrating could easily create error in some meters.

 

[renthispace]

I was going to recalibrate it tonight, but I didn't. I only tested the buffer solution to see how far off my pH pen drifted in two days, which turns out was not that much. I calibrate with 3 points of solution, 4, 7, and 10.

 

[ajdelange]

So I was going to recalibrate my meter when I decided to see how far off it currently was. pH 4 buffer read 4.01 @17C (bottle says 4.00) and pH 10 buffer read 10.09 @ 17C (bottle says 10.08 when interpolated).

Amazing my Pocket Pro is only .01 off from calibration that I did two days ago. Meaning my readings were likely correct?

Most likely, yes. We can concoct a bizarre situation in which you were off by 0.3 on brew day and in the following two days the thing drifted into near perfect alignment. Possible but very improbable. It is, nevertheless, always good practice to do a buffer check a few minutes after calibration and at the end of the brew day.

Anyway I read the pH of the fermenting beer and it was 3.91 @18.6C!

Now that is suspicious as beer usually finishes in the 4's unless it is a sour beer. Some ales/stouts will finish under 4. I'd do another cal check (4 and 7) and recal if necessary and check that again.

So either my GH & KH test kit steared me wrong or maybe my grain bill is different than what I thought? Still seems like I'm off _a_lot and these two issues would only account for minor error (as one would expect there to be).

Yes, a discrepancy of 0.3 is worth exploring.

 

[ajdelange]

Wait! Why are you calibrating with 4 and 10 solutions? For the typical pH range in brewing, you should calibrate with 4 and 7 solutions. The way you are calibrating could easily create error in some meters.

Turns out he didn't calibrate with 4 and 10 only but rather with 4, 7 and 10.

The fundamental requirements for best accuracy are that the buffers span the range of pH's you intend to measure. If you are only measuring mash pH then there is no need for the 10 buffer measurement as 4 to 7 includes all likely mash pH's. The best measurments are obtained half way between the pH values of the buffers you use and are actually better than the buffer tolerance the closer to the half way point you get. For example, at pH 5.5 (right in the range we are interested in) you can expect buffer induced error of 0.02/sqrt(2) = 0.014 for buffer with a tolerance of ±0.02 (most of them). As you approach the pH of either buffer the error increases to the buffer tolerance (± 0.02) and as you go outside it continues to increase so that for example at pH 8.5 you might expect error of 0.028. You would be better off if you did the three point calibration with 10 buffer in which case at 8.5 you might expect 0.014 again if, and this is a big if, you are sure of the 10 buffer which, being at high pH, is unstable because it captures CO2 from the air and its pH drifts downward. You might be better off outside at 4 - 7 cal with good buffers there than with a 7 - 10 cal using an 10 buffer that is not fresh.

How about a 4 - 10 cal.? No reason not to use it based on what we have discussed so far. Theoretically the accuracy would be about half way between ±0.02/sqrt(2) and ± 0.02 at either pH 5.5 or 8.5. Theoretically here assumes linearity of the electrode response. Real electrodes are, of course, not completely linear and that is why multi buffer calibrations are done. If you really want to be certain when measuring mash pH you would calibrate with buffers of pH 5 and pH 6. Some meters will let you do this. Others insist that you use standard buffers.

 

[renthispace]

Just did another test on the meter. I still have not recalibrated since Sunday. pH 4 solution read 4.01 (.01 off again) and the pH 7 read 7.03 which is what is specked on my buffer solution.

I just tested the beer again and got 3.94.

I also re-tested my GH & KH and I got the same number of drops and associated values as I did last time.

I am going to brew again this weekend. It will be slightly darker than this brown (a porter). I hope this issue can be figured out so I don't do it again.

 

[renthispace]

So at this point is it safe to rule out issues with my pH pen?

I went back to the brew shop yesterday to buy ingredients for my Porter I'm planning on this weekend and updated the lovibond for the grains that I used in this Brown.

Brewersfriend still says I should have added 56ml of phosphoric acid to get me to 5.4

The only way I could get the calculator to mirror what I experienced was to make the Ca ions read 200 and or really reduce the alkalinity. With my 20ml added acid it projects the pH to be 5.27 (very close to what I measured during mash). I just can't imagine my Ca is 200, since I re-ran the GH & KH test several times. Also my water report says the range of Ca is 34-66, Mg 9-13, and hardness 50-144; the GH & KH test results fall within that range.


So if its not my pH pen, my water, or my grains, what could it be? Just chalk it up as a fluke? Unless someone has a better idea for my next brew I am going to hold off any acid additions until I test the mash pH 15 minutes in. Brewersfriend says I should add 66ml to my Porter to reach 5.4, and its similar to this recipe.

 

[ajdelange]

The smart money makes a test mash in which about a pound of your proposed grist is mixed with about a quart and a half of your water treated as you plan to treat it and heated to dough in temperature, holds the mix at near dough in temperature for about 15 minutes, cools a sample of the liquid to room temperature and checks the pH. If things are way off you can adjust acid additions and try again.

 

[renthispace]

I agree a test mash is the best way to know whats expected during the real mash, I'm just trying to save time and get close enough. That's why we estimate via these calculators; get close and adjust accordingly.

If I have another brew that is way off on the calculated pH, I'm going to take that tap water and send it in to get it tested. I really just wanted to confirm I wasn't missing something (in the calculator, water adjustments, etc). Looks like I'll just have to experiment more and see if I can find what caused the error.

 

[ajdelange]

Is the acid really 10% ?

I was getting really wacky results with 10% Lactic acid, high and low. A chemist told me I should stir the acid before I use it. Apparently the water would separate out giving me random strength when I poured it.

It worked for me.

I didn't know much about this when Martin asked if I had ever heard of it but in the quest for information about the pK of lactic acid at temperature other than 20 °C (anyone have any data on this?) I stumbled across a phase diagram for lactic acid solutions. At 10% the freezing point is about -2 °C so you shouldn't have any separation at room temperature. Now, OTOH, if you had an 88% solution of either straight D or L the freezing point is about 26 °C and you would expect separation at room temperature. But we don't buy D or L, we buy a racemic mixture. Looking at the melting point of pure D or L lactic acid, around 52 °C and comparing that to the melting point of a DL mix which is about 10 °C I conclude, which I probably don't really have the right to do, that the freezing point of a racemic 88% solution would be about 26 - 42 = -16°C but as the phase transition line above the eutectic point is pretty linear for D or L I'm guessing it's probably pretty linear for the mix too. In any event a couple hours in my freezer at -20 °C doesn't freeze the 88% lactic I bought at the LHBS. If nothing else this demonstrates this it is indeed DL Lactic acid.

 

[jsguitar]

To the OP. For what it's worth, I've been finding that the BF advanced water calculator is predicting my mash ph .08-.1 higher than what actually occurs consistently. There are a lot of factors involved so I'm not sure what is happening but I'm just going to assume that if I'm shooting for 5.4 that I'll get the calculator to more like 5.5. I typically use 90% RO, 10% tap, minerals, and often phosphoric acid. I have a good small digital scale for the minerals so I don't think it's that. I thought it might be the acid, but on the last batch I didn't use any and I had the same issue. Could be the variability of the bit of tap water I use, the variability of malts, ect. I also use the Hach meter and calibrate every time and I'm confident that it's not the issue.

I like AJ's test mash idea but I never get around to doing it! I'm brewing tomorrow so maybe I'll do a test this evening.

 

[ajdelange]

If you are getting better than 0.10 (and I am assuming here that you mean 0.08 - 0.10) especially as a consistent bias then you are doing very well indeed.

 

[jsguitar]

If you are getting better than 0.10 (and I am assuming here that you mean 0.08 - 0.10) especially as a consistent bias then you are doing very well indeed.

Thanks AJ, yep that's what I meant. That's good to hear but I'd still rather not be at 5.3 when I'm shooting for 5.4. At least it has been consistent, so easy to correct going forward.

I haven't used bru'n water in a while because I tend to use my iPad now and brewer's friend works with that, but I'm going to start comparing the two to see what I find.

 

[jsguitar]

So much for a consistent bias. I did a test mash last night and achieved a mash ph of 5.54 with no acid. Predicted ph by brewer's friend? 5.55. I added about half the acid today that the calc. predicted I'd need at the beginning of a protein rest and I ended up needing the whole amount so I added it during the beginning of the sacch. rest. This one was spot on. I'll try doing the test mash in the future on new brews again. It seems to be the only way to know for sure.

 

[renthispace]

Nice to hear the calculator working for you jsguitar. I'm guessing my water source isn't what I think it is.

I was closer on this brew over the weekend. Brewersfriend predicted 5.78. I pulled a sample at 15 min but it took forever to cool down (forgot to leave the shot glass in the freezer). I finally read it at +30 minutes in the mash and got 5.70. Pretty dang close. The original calculation said I should have added 66ml acid, I only added 55ml. At 45 min into the mash I read pH again and got 5.00.

I'm guessing this lower value is partially because my acid was added much later into the mash than it should have? And/or my issue could be because the way my system recirculates. I dumped the acid into my inner pot but there is additional liquid in the outer pot (which is recirculated). I know there would be a time delay for the pH to settle once I add the acid. I should have tested it again at the end of the brew to see what it was but I got distracted.

I'm probably going to get a lab result of my water just to see how far off my estimates are.

 

[reuliss]

Renthispace, I'm having the exact same issue as you, except I used a LaMotte kit to test my water and use lactic instead of phosphoric. What's worse is that, for me, sometimes my tested ph is over the prediction and other times is is below. So frustrating.