ph meter vs software discrepancy

[jodyer]

Hi there.
I'm new to the water adjustment game, and I'm sorting out some differences in my mash pH with regard to the predicted pH with BrunWater vs my actual measurement.

For my past 3 brews, below, have given me an average variance of -0.31 from the predicted amount. ie
Brown Ale: predicted = 5.39; actual= 5.1; difference = 0.29
Saison predicted = 5.53; actual= 5.08; difference = 0.45
Porter: predicted = 5.3; actual= 5.1; difference = 0.2

With all that can effect mash ph, should I continue to look for errors in reading/meter taking, or should I accept the variance assume the software output will be 0.3 above the real result and plan on overshooting the theoretical pH? I'm also open to my water source changing, and thus, my chemistry, including alkalinity.

I got a Wards lab analysis of my water, using a Thermoworks pH meter (model 8689) that states a +/- 0.05 accuracy, and use BrunWater for my software. I calibrate before every reading, sometimes twice, as I'm still trying to get into the swing of all the measuring. Between brewdays, the electrode is in a storage solution. I run my water through a carbon filter and tx with campden, add the minerals the night before (except lime, as I mix it in the mash). I don't use chalk.

Sample is pulled 15 and 45 minutes into mash and chilled to room temp in a shot glass. The meter is usually soaking in tap water between measurements. I do not dry it between measurements, just rinse it, and have only been using tap water, not distilled/deionized.
If needed: my wards lab readout for Henrico, VA = Ca 48, Mg 7, Na 43, S04 99, Cl 26,
Bicarbonate 120;

Thanks for the input
JD

 

[thehaze]

The initial pH reading at 15-20 minutes from mash start will always be lower, as the pH rises during mash, hence at the end of a 60-90 minutes mash, the pH will be higher.

Regarding your readings: A saison requires a very simple recipe, thus you probably had some Pilsner/Pale Malt and some other base or crystal malt. This means, at some point you might had to adjust the pH with Lactic Acid or Phosphoric Acid, to bring it down. What I like to do is mash in all my grains and after 10 minutes get a pH reading and then adjust with Acid.

With dark beers, you would probably not have to adjust at all or you will need to add baking soda to raise the pH. Roasted grains and Crystal malts are highly acidic and will drive the pH down quickly. The pH levels given for each type of grain in BrunWater is fairly general, as you could easily have a base malt which has a lower or a higher pH than the spreadsheet is guessing. This too will affect the pH.

 

[ajdelange]

When you throw water into grain and take a pH reading you are essentially getting the pH of the water as it takes some time for the water to penetrate the grain and react with it. Thus if you have added acid to the water (which given your alkalinity you probably did) initial pH readings will be low and rise but if you added alkali (dark beer) it will initially be high and fall. It will also fall if you have a lot of calcium in the water as that take some time to react too.

That said the rises you are seeing are not atypical but you also need to understand that no spreadsheet is going to guarantee estimates that are better than ±0.2 pH in all cases. And yes, you should definitely check your pH meter's stability (see the sticky on pH meter calibration at the top of this thread).

 

[Silver_Is_Money]

Are you noticing any consistent pH difference between the readings of samples pulled at 15 minutes and those pulled at 45 minutes into the mash?

The probe should be rinsed in distilled water and dried off before taking readings. I don't see this as being the source of your problem though.

 

[bitteritdown]

You could set aside the spreadsheet and employ a simple water treatment:

1.) Measure alkalinity with a test kit (salifert, etc..)
2.) Measure calcium with a test kit (salifert, etc..) (or multiply the alkalinity by 0.4)
3.) (1,2 And/or) Set the pH (and thus alkalinity level) of all liquor to a reasonable level for the style being brewed
4.) Increase calcium (and thus sulfate / chloride) to a reasonable level for the style being brewed
5.) Select a reasonable pH or reference Murphy and Sons tables or Brupaks tables for alkalinity and mineral levels per style

Employ the Sparge Water calculations of a spreadsheet to determine how much acid to add to the liquor to establish the target pH or write your own program using formulas provided by AJ Delange. These are the exact same formulas used in the popular spreadsheets.

The "test and guess" method also works to establish a reasonable pH level. (That is add small amounts of acid to the liquor until it reaches the desired pH.)

Reading Kai Troester's paper on the SRM model employed in these spreadsheets will give you an idea of how those spreadsheets work and why they're not as accurate as you expect.

 

[ajdelange]

3.) (1,2 And/or) Set the pH (and thus alkalinity level) of all liquor to a reasonable level for the style being brewed

This is a great way to do things if the grist is such that an acid addition would be required were the beer brewed with DI water. In the converse case (dark beer) where alkalinity is required to neutralize the acidity of the high kilned malts in a DI water mash you would have to add this alkalinity after you have added the acid to the water and that doesn't make much sense. You can, of course, still use this liquor acidification method buy you would have to modify the technique. One way to do this is to acidify the water keeping track of how much acid you used. Then calculate the amount of alkali needed for the grains (in mEq), remove the amount of treated water from the liquor tank to which the calculated number of mEq of acid has been added and replace it with untreated water. I think we need an example here. We treat 100L of water with 80 mEq of acid to get it to pH 5.4. We find that we need 40 mEq of alkali for dark grains. Remove 50 L of treated water and replace it with untreated water. In some cases we may need to remove all or nearly all the treated water and this approach is impractical. In those cases we would need to use the more traditional methods of calculating the alkali addition and not acidify the water at all.

5.) Select a reasonable pH or reference Murphy and Sons tables or Brupaks tables for alkalinity and mineral levels per style

Stay away from these tables unless you are sure that you want a beer that conforms with the traditional British style ales. Do not use these recommendations for lagers. Murphy's recommendations result in what would in most cases be considered insane levels of mineralization. If you are sure you want that then fine. If not then consult a source like the Brewers Publications monographs or ask here about reasonable mineralization levels. Several of the popular spreadsheets have 'profiles' for various styles.

Employ the Sparge Water calculations of a spreadsheet to determine how much acid to add to the liquor to establish the target pH or write your own program using formulas provided by AJ Delange. These are the exact same formulas used in the popular spreadsheets.

While there is nothing wrong with the formulae at that link there are ones at https://www.homebrewtalk.com/forum/threads/calculating-bicarbonate-and-carbonate.473408/ that are easier to understand. The amount of acid needed per liter is, in terms of the formulas at this link C*(Q(pHz) - Q(pHs)) where pHz is the pH you want to reach and pHs is the source water pre treatment pH. Note that you need to know the alkalinity and pH of the source water to use these formulae.

The "test and guess" method also works to establish a reasonable pH level. (That is add small amounts of acid to the liquor until it reaches the desired pH.)

If you overshoot (i.e. add too much acid) just add more water until pH gets back up where you want it.

 

[jodyer]

My thanks for all the smart answers. Looks like I have some more reading and experimentation ahead of me.
I am using lactic acid (in the mash water, and sparge water) as my main acid, and canning lime to alkalize (added into the mash) to pull my ph up or down as needed. Interestingly, my mash pH stays about the same at 15 vs 45 minutes in.

Since my true mash pH is consistently 0.2 points under my software estimate, should I compensate with acid/lime to get it to the right pH. In other words, If my target is 5.4, should I adjust the software to give me a pH 5.6, and fall that 0.2 points shy? Or does the nonlinear nature of pH not make it that simple?

Lastly, when looking at bicarb in a water profile - since bicarb's impact is mainly on the mash pH, I'm assuming any adjustments are for the pH level and not a particular bicarb level, like we would adjust for a particular calcium or so4 level... Correct?
Thanks for the input.
JD

 

[bitteritdown]

Since my true mash pH is consistently 0.2 points under my software estimate, should I compensate with acid/lime to get it to the right pH. In other words, If my target is 5.4, should I adjust the software to give me a pH 5.6, and fall that 0.2 points shy? Or does the nonlinear nature of pH not make it that simple?

No, do not adjust your pH up 0.2 points.

What is the P value of your consistence statistic? How many data points have you used to arrive at that conclusion?

0.2 is within the accuracy (+/- 0.05) of your pH meter.

Check your pH meter stability. Preferably think about obtaining a (+/- 0.01) accuracy pH meter ( a more accurate pH meter ).

Lastly, when looking at bicarb in a water profile - since bicarb's impact is mainly on the mash pH, I'm assuming any adjustments are for the pH level and not a particular bicarb level, like we would adjust for a particular calcium or so4 level... Correct?
JD

Not sure what a teaspoon of bicarbonate tastes like but yes, anion/cation balance and pH are the functions of most interest to brewers.

 

[ajdelange]

Since my true mash pH is consistently 0.2 points under my software estimate, should I compensate with acid/lime to get it to the right pH. In other words, If my target is 5.4, should I adjust the software to give me a pH 5.6, and fall that 0.2 points shy? Or does the nonlinear nature of pH not make it that simple?

The first thing you might want to try is different software. Just seeing the variability between the estimates the different programs give should be instructive.

That aside, clearly whatever the software you are now using is telling you to add more acid than you need or to add too little base. Adjust the acid or base amount until a test mash shows you a pH near 5.4.

Lastly, when looking at bicarb in a water profile - since bicarb's impact is mainly on the mash pH, I'm assuming any adjustments are for the pH level and not a particular bicarb level, like we would adjust for a particular calcium or so4 level... Correct?

Yes, that is correct. A pH that is too low means that there are too many hydrogen ions (H+) in the mash. The sole purpose of added bicarbonate ions is to absorb some of those excess ions. What happens is H+ + HCO3- --> H2CO3 --> CO2 + H2O or, in words, an H+ ion combines with a bicarbonate ion to form a molecule of carbonic acid. This decomposes into CO2 which escapes to the atmosphere because of the elevated temperature and stirring of the mash. Thus in doing its job the bicarbonate ion is removed from the mix.

As someone pointed out to me at beer pH there is more bicarbonate in solution from the gas used to carbonate the beer than there is from the brewing water even if it were quite alkaline.

 

[ajdelange]

Not sure what a teaspoon of bicarbonate tastes like...

Easy enough to find out but the answer is that it doesn't taste very good. However, as pointed out in #9 almost all the bicarbonate added removes itself as long as the addition does not raise the pH too high. The amount of bicarbonate remaining in mash/wort/beer does depend strongly on pH. The lower the pH the less bicarbonate.

 

[mabrungard]

I trust you are mixing all acids and minerals into your WATER before adding your grain? If those materials are added to the mash and then you are trying to stir them in, its unlikely to achieve homogeneity and that will affect pH.

I see from the water report that there should only be a rare need to add alkalinity to that tap water. How consistent is the quality of that water source? The measured results suggest that the alkalinity has dropped from the what is reported.

 

[safcraft]

There are many experienced users here giving valued advice.
Still i can offer you mine:

- First calibrate you PH meter with buffer solutions. This will tell you if the meter is off or not. This is essencial otherwise you are just guessing.

- Then try to play with the BRUN water spreadsheet water inputs because a little off can influence the end result in PH prediction. I know i had the same (0.2 difference) and this was due to my water analysis was off to the real water values.

I since calibrated the spreadsheet and i am in +-0.03 precision with the BRUN water prediction. This makes a huge difference in mash efficiency.

Regarding your values, i would say that either your PH meter is not calibrated, OR , you have a much LOWER alcalinity than what you inputed in your BRUN water spreadsheet.

This was my case, i lowered the alcality and now need much less acid to reach my PH goal.

All the best of luck

 

[ajdelange]

- First calibrate you PH meter with buffer solutions.

Good point! Also do a stability check. See the sticky at the top of this forum.

Regarding your values, i would say that either your PH meter is not calibrated, OR , you have a much LOWER alcalinity than what you inputed in your BRUN water spreadsheet.

Or that one or more of the malts you are using has lower DI mash pH and/or buffering capacity than the spreadsheet models them as having.[/QUOTE]

 

[mabrungard]

AJ, I don't think that its likely that a malt's buffering or DI pH would create the degree of error displayed here, unless it was user error. Since the result seems to be systemic, I'm less inclined to assume user error.

 

[ajdelange]

Neither do I. I did mean to mention input error but it slipped my mind. Or perhaps electrode instability.